Design of a Typhoon-Resistant Multi-Span Greenhouse with an Elevatable Roof for Tropical Regions

Abstract

Agricultural facilities in tropical regions such as Hainan China face dual challenges from summer typhoons and occasional winter cold waves. Traditional greenhouses are generally constructed at a low height to resist typhoons, which hinders mechanized operations, while the use of insect-proof screens compromises thermal insulation. To resolve these contradictions, this study designs a typhoon-resistant multi-span greenhouse with an elevatable roof. Its core innovation lies in adopting a mechatronic steel cable system to achieve synchronized elevation of single-span roof surfaces. During daily operations, the roof is elevated to facilitate mechanized field operations; during typhoons or cold waves, the roof is lowered to the ground, reducing wind load impact and improving thermal insulation performance. The greenhouse’s elevating system incorporates multiple safety functions, including bidirectional self-locking and overload protection. Structural calculations using PKPM 2010 software show that under two working conditions—roof elevated (basic wind pressure of 0.45 kN/m²) and roof lowered (basic wind pressure of 1.30 kN/m²)—all indicators meet the requirements of relevant codes. Compared with an ordinary circular-arch greenhouse of the same size and under the same loads, the steel consumption of the standard single-span frame (6 m span, 4 m bay width) of the Elevating Greenhouse is only 67.38 kg, a 35% reduction compared with 103.58 kg for the ordinary greenhouse, significantly reducing construction costs. This study provides an innovative, safe, and economical technical solution for protected agriculture in tropical regions.

1. Introduction

As a core component of modern agricultural facilities, greenhouses are widely used in agricultural production due to their simple structure, low material consumption, ability to resist extreme climates (e.g., low temperatures, heavy rains, and typhoons), and effective regulation of crop growth cycles and growing environments [1,2]. Compared with conventional open-field production, protected agricultural production enables year-round crop output and improves the annual supply guarantee rate of vegetables and fruits.

Hainan Province, China, features mild temperatures and low rainfall in winter and spring, making it China’s largest production base for winter melons and vegetables. However, high temperatures, heavy rains, and frequent typhoons occur in summer and autumn; open-field crop production is severely restricted by multiple meteorological factors (high temperature, high humidity, and waterlogging) and biological factors (e.g., diseases and pests). While agricultural production using facilities can effectively overcome various adverse external conditions, common greenhouses in Hainan, China, generally have relatively weak structural wind resistance and excessively high construction investment costs. In contrast, economical facilities suffer from insufficient wind and rain resistance performance and lack winter thermal insulation functions. Therefore, a production demand for greenhouse structures has emerged in practice—structures that can resist typhoons, prevent rainwater damage, and simultaneously achieve cold wave protection functions in winter according to weather conditions.

The design of greenhouse structures is often controlled by stiffness and stability, and they are highly sensitive to wind and snow loads and their distributions, though snow load is negligible in the study area (Hainan, China) due to its tropical climate, unlike industrial and civil building structures, which are controlled by strength [3,4]. In recent years, frequent typhoons in tropical coastal areas have caused numerous wind-related disasters, damaging large numbers of greenhouses and resulting in significant agricultural economic losses [5,6]. Typhoon Ketsana (2009, No. 16), Typhoon Conson (2010, No. 2), and Typhoon Son-Tinh (2012, No. 23) caused damage to a large number of greenhouse structures in southern Hainan [7]; Super Typhoon Rammasun (2014, No. 9) inflicted devastating damage to 467 hectares of greenhouse structures in northern Hainan [8]; Severe Typhoon Sarika (2016, No. 21) destroyed 15.67 hectares of greenhouses in Yunlong Town, Haikou City, and 2.15 hectares in Wanning City [9]. Most recently, Super Typhoon Yagi (2024, No. 11) dealt a devastating blow to agricultural facilities in Hainan Province. Particularly in Northern Hainan, the destruction rate of facility greenhouses exceeded 80%, affecting 8,851.04 hectares of crops and causing direct economic losses of approximately 5.12 billion Chinese Yuan [10]. Wind load has thus become the main controlling load in the design of greenhouse projects in coastal areas. To improve the wind resistance of greenhouses, scholars from China and other countries mainly adopt a technical approach centered on resisting wind loads via structural parameter optimization and morphological innovation, with research focused on three key aspects. Firstly, scholars have explored the effects of structural parameters using numerical simulation. For example, Hou, L.W.; Wu, W. [11] systematically analyzed the impacts of key parameters—including greenhouse height, front roof shape, and structural frame spacing—on greenhouse structures; Cai, W.Y. [12] focused on the group effect, simulating the surface wind pressure of circular-arch greenhouse groups under different wind directions and arrangements, which provided a basis for optimizing group layouts. Secondly, detailed calculations of structural mechanical properties have been conducted using finite element software. For instance, Ren, J. [13] used ANSYS software to study three key mechanical indicators of greenhouse structures (i.e., stress, displacement and instability status), finding that structural safety is related to structural stiffness and strength; Emekli et al. [14] also employed the finite element method to systematically analyze the stress characteristics of greenhouse structures under different load conditions (e.g., wind load), and proposed specific structural optimization suggestions based on their findings; Liu, Y.F. [15] established a finite element model of a truss-arch light-steel plastic-covered greenhouse, realizing the optimal design of frame parameters by calculating stress and displacement. Thirdly, the development of new structural morphologies with enhanced wind resistance has been a focus of research. For example, Kwon [16] studied large-span dome greenhouses, revealing the wind pressure distribution law under strong winds and the areas prone to local damage, and emphasized that the bending moment caused by strong winds must be considered in structural design; Xu, Y.Q. et al. [17] found through comparison that greenhouses with an M-shaped roof exhibit better wind pressure characteristics at all wind angles; Zhang, S. et al. [18] demonstrated that truss arches show superior wind resistance compared to single-tube arches under 0° wind direction. Furthermore, experimental studies have provided crucial support for deepening the understanding of wind load characteristics on greenhouse structures and for validating new structural morphologies. For instance, Robertson et al. [19] investigated the influence of different cladding types (permeable and impermeable) on the wind pressure distribution over structural surfaces through wind tunnel tests, providing an experimental basis for the accurate assessment of wind loads on greenhouse structures. Scarascia-Mugnozza et al. [20] designed and tested an innovative lightweight greenhouse prototype based on the tensegrity concept, experimentally verifying the feasibility and mechanical performance of this structural form, thereby opening new avenues for the morphological innovation of wind-resistant greenhouse structures. Yan, J.Y. [21] proposed a basic wind pressure calculation method specifically designed for greenhouses, which has been verified through practice to be applicable to the design and practical application of plastic-covered greenhouse structures.

While the aforementioned studies have improved the wind resistance of greenhouses, their structural morphologies are fixed after construction and still have limitations under extreme wind loads. To address this, Chinese scholars have proposed various greenhouse structures featuring elevable roofs. Several representative designs developed by Chinese institutions and individual researchers are outlined below: Xi’an Nongsheng Industry Co., Ltd. (Xi’an, China) [22] proposed an Elevating Greenhouse driven by a winch and steel cables; however, it requires high roof stiffness, and the position-fixing method during elevation is not clearly defined. Hainan Lintian Agriculture Co., Ltd. (Haikou, China) [23] designed an automatic elevating structure that achieves position fixing via structural sleeves and bolts, which improves the operational stability of the structure. Nevertheless, its operation is rather cumbersome in large-area application scenarios. Hong, G.Y. [24] drew on the sliding principle of curtain structures and proposed a typhoon-resistant, easily Elevating Greenhouse, with bolts and sockets installed on the side of columns to control the roof height. Hefei Jianye Greenhouse Co., Ltd. (Hefei, China) [25] designed a Y-shaped support structure whose height can be adjusted via a screw, based on the umbrella opening-closing mechanism, and it exhibits a certain level of self-adaptive adjustment capability. While these studies exhibit unique features in the implementation of elevating mechanisms, there remains room for improvement in structural simplicity, operational convenience, and adaptability to large-area application scenarios. From an international perspective, there have also been relevant explorations into greenhouse structural innovation aimed at enhancing climate adaptability: The Dutch Venlo-type greenhouse represents the pinnacle of standardized, high-efficiency controlled environment agriculture, yet its fixed structure offers limited adaptability to extreme weather events [26]. Japan has explored passive adaptation strategies, such as integrating agricultural production into building envelopes like Trombe walls; this approach focuses on energy savings but may lack the rapid response capability required to cope with typhoons [27]. Advances in South Korea concerning building-integrated rooftop greenhouses and automated vertical farms emphasize energy synergy and labor efficiency, yet their structural design paradigms are not primarily aimed at typhoon resistance [28].

Against this background, this study innovatively proposes a typhoon-resistant multi-span greenhouse with an elevable roof for tropical regions (e.g., Hainan, China). By means of a mechatronic active control mechanism, this structure lowers the roof to the ground before typhoons arrive in summer and autumn, reducing both the windward height and the impact of wind loads. Only the greenhouse roof structure bears the wind loads, which can greatly reduce the steel consumption of greenhouse components such as columns. Lowering the roof to the ground does not impair its rainstorm-proof function, enabling the greenhouse to achieve both typhoon resistance and rainstorm protection. In winter, when cold waves occur, the roof can also be lowered to form a closed structure, which improves thermal insulation performance and protects crops inside the greenhouse from harm, ultimately achieving the coordinated optimization of disaster prevention performance and economic efficiency.

The structure of this paper is as follows: Section 1 elaborates on the challenges of typhoons and cold waves faced by greenhouses in tropical regions, the research status at home and abroad, as well as the objectives and innovative directions of this study; Section 2 introduces the greenhouse structure and design parameters, the design of key systems (elevating system, self-locking mechanism, sliding elevating device), and the load calculation method; Section 3 presents the results of mechanical analysis of key components, displacement analysis, and comparative analysis with ordinary circular-arch greenhouses; Section 4 discusses the innovation of the design paradigm, technical advantages, highlights of safety assurance, as well as the limitations of the study and future prospects; Section 5 summarizes the core conclusions of this typhoon-resistant multi-span greenhouse with an elevatable roof in terms of structural innovation, system safety, and economy, along with its application value for protected agriculture in tropical regions.

2. Materials and Methods

2.1. Design of Greenhouse Structure and Parameters

In accordance with the Chinese National Standard Design Standard for Agricultural Greenhouse Structures (GB/T 51424-2022) [29] and the method for determining overall greenhouse dimensions proposed by Tong, G.H. et al. [30,31], this study further integrated three practical requirements into the greenhouse design: the agronomic needs of leafy vegetable cultivation in tropical regions (e.g., Hainan, China), the technical demands of the elevating mechanism on the roof arch, and the operational considerations for facilitating field mechanized operations. Based on this, the greenhouse was designed with: span = 6 m, bay spacing = 4 m, shoulder height (internal clear height) = 3 m, and outer frame height = 4.5 m. The entire greenhouse roof is covered with a 0.12 mm-thick polyethylene film (film thickness can be dynamically adjusted according to wind load levels) to achieve top sealing and rainproofing functions. The four side facades of the greenhouse are equipped with 40-mesh insect-proof screens [32]—a mesh size effective for blocking common tropical pests (e.g., aphids, thrips) that threaten leafy vegetables, while ensuring adequate ventilation and preventing pest intrusion. The 40-mesh insect-proof screens are fixed to the side columns, forming permanent vertical walls. The elevatable roof structure moves vertically within the space enclosed by these screens. A defined gap is reserved between the moving roof edge and the fixed insect-proof screens to prevent contact, damage, or wear during the elevation process. Furthermore, to effectively manage rainwater when the roof is lowered during typhoons, a drainage system is integrated into the gutters of the multi-span greenhouse, effectively preventing indoor water accumulation and crop flooding. The parameters selected in this design aim to balance structural stability, mechanized operations, and wind load response; the subsequent analysis will verify their rationality. The key design parameters are listed in

Table 1. Key Design Parameters of the Elevating Greenhouse.

Parameter	Value	Unit
Span	6	m
Bay Spacing	4	m
Shoulder Height	3	m
Outer Frame Height	4.5	m
Roof Film Thickness	0.12	mm
Insect-Proof Screen	40	mesh

. A structural diagram of the Elevating Greenhouse is shown in Figure 1. The key material properties are provided in

Table 2. Key Material Properties.

Material	Property	Value	Unit
Q235 Steel	Yield Strength	235	MPa
Polyethylene Film	Thickness	0.12	mm
Insect-Proof Screen	Mesh Size	40	-
Stainless Steel Wire Rope	Breaking Load	≥8.9	kN

.

This Elevating Greenhouse is innovatively designed based on the structure of a conventional circular-arched multi-span greenhouse. Its main frame adopts an assembled structure of hot-dip galvanized steel pipes, forming a spatial frame system consisting of columns, horizontal and vertical beams, and independent foundations. Within this frame structure, the circular-arched roof performs vertical elevating movement along the axial direction of the columns. The external support integrates a motor-driven device, a pulley block, and an elevating mechanism, which are anchored to the foundation via rigid anchor bolts—ensuring the stability of power transmission for roof elevation. This “rigid frame-flexible interface” coupled design enables the facility to possess both structural stability and environmental adaptability.

2.2. Key System Design

2.2.1. Elevating System Design

As the core functional module of the Elevating Greenhouse, the elevating system is designed to achieve smooth, precise, and safe vertical operation of the roof structure. It also balances power transmission efficiency, structural stability, and environmental adaptability.

Principle of the Elevating System: The mechatronic steel cable electric elevating system adopted in this study is based on a three-level architecture system of “power drive—mechanical transmission—execution feedback” (the overall control architecture is shown in Figure 2). Through the collaborative work of multiple subsystems, the rotational motion output by the motor is converted into the vertical movement of the roof unit. Its working principle can be analyzed from three aspects: the power transmission mechanism, the motion conversion logic, and the safety assurance mechanism.

Power Transmission Mechanism: Power transmission is the foundation of the elevating system, with its core being the use of a multi-stage transmission mechanism to achieve efficient power transfer and torque adjustment, ensuring stable and controllable power output during the roof elevating process. The system’s power source is a gear motor, which transmits power to both sides via the drive shaft. The motor’s elevating capacity is no less than 1300 kg; the output shaft end is equipped with a sprocket (08B, 28 teeth, outer diameter: 117 mm), while the drive shaft is fitted with a sprocket (08B, 18 teeth, outer diameter: 77 mm). The transmission process unfolds as follows: When the gear motor is activated, its rotational power is initially conveyed to the sprocket, and the chain then transfers this power to the drive shaft. Self-locking mechanisms are strategically placed along the drive shaft. These mechanisms are welded to the drive shaft, allowing them to rotate together. Each self-locking mechanism incorporates a gear reduction module (module 2, with 31 teeth). Secondary deceleration occurs through gear meshing, which amplifies torque to meet the heavy-load demands of roof elevating while ensuring consistent power distribution.

Motion Conversion Logic: The core function of the elevating system is to convert the rotational motion of the drive shaft into the vertical elevating motion of the roof. This conversion process is achieved through a mechanical combination of “self-locking mechanisms, stainless steel wire ropes, and pulley blocks,” and its motion conversion logic is based on the “rope-pulley transmission principle.” The details are as follows: Ascending motion: The gear motor rotates forward, and the drive shaft drives the self-locking mechanisms to rotate clockwise in synchrony. At this time, the stainless steel wire ropes wound around the self-locking mechanisms are tightened. One end of each wire rope is fixed to a self-locking mechanism, and the other end is connected to the sliding elevation device after changing the force direction via a Deflector Pulley. Since the length of the wire rope is fixed, the process of winding the rope onto the self-locking mechanism exerts an upward pulling force on the sliding elevation device, which in turn drives the roof and its covering materials to rise vertically along the axial direction of the columns. To ensure synchronous elevation of the four roof corners, each roof arch (6 m span, 4 m bay width) is equipped with an independent “self-locking mechanism-wire rope” transmission unit, with the self-locking mechanisms having the same diameter and the wire ropes the same length across all transmission units. The wire ropes are wound in a single layer, which can effectively prevent roof tilting or jamming. Descending motion: The gear motor rotates in reverse, and the bidirectional self-locking device inside the self-locking mechanism releases the lock. At this time, the wire rope gradually loosens, and the roof descends vertically along the axial direction of the columns under its own weight until it reaches the limit height and stops. Stopping: When the roof reaches the limit height, or the power is manually cut off, or an obstacle during operation causes an overload that triggers the thermal relay to stop, the motor enters a stopped state, the self-locking mechanism engages, and the roof hovers at its current position.

Safety Assurance Mechanism: The elevating system fully accounts for potential risks during the design process. In this study, a multi-layer safety assurance system is established, consisting of electrical protection, self-locking mechanisms, and physical limiting. First, the gear motor is equipped with a normally closed brake, which responds instantaneously upon power failure to achieve mechanical braking, locking the power output at the source. Second, a thermal relay is installed in the motor circuit (the rated current is determined by the motor power; in this design, the motor has a rated power of 0.8 kW, and the thermal relay is set to a rated current of 3.5 A). When the motor temperature exceeds the set threshold (120 °C) due to overload, the thermal relay automatically disconnects the circuit to prevent motor burnout. Third, the drive shaft of each roof unit (6 m span, 4 m bay width) is independently equipped with a bidirectional self-locking mechanism, whose internal ratchet-pawl device enables locking at any position. This design ensures that if no more than 50% of the self-locking units fail accidentally, the remaining units can still independently bear the load of the entire roof, resulting in a high safety factor. Fourth, limit stops and manual hooks are installed at the upper and lower limit positions of the guide rails to ensure the safe operation of the roof.

Layout of the Elevating System: The layout of the elevating system is designed by considering the greenhouse’s overall structural dimensions, force-bearing characteristics, and functional requirements. It follows the principles of “balanced force bearing, convenient installation, easy maintenance, and high space utilization” to ensure all components work in coordination, enabling the smooth elevation of the roof. The gear motor is arranged along the span direction of the greenhouse, in the central area of longitudinal columns, to ensure balanced power output. The drive shaft, made of hot-dip galvanized steel pipe with dimensions of φ 50 mm × 3 mm, is also arranged along the span direction. Both ends of the drive shaft are fixed to the longitudinal columns via bearing block supports, extending through the entire length of the greenhouse. These bearing blocks serve to enhance the stiffness of the drive shaft and prevent bending deformation caused by the increased span. Self-locking mechanisms are installed every 4 m along the drive shaft, with uniform spacing between each mechanism to avoid mutual interference among the wire ropes.

In the transmission design of the elevating system, the bay-direction length controlled by a single drive unit must be limited to ≤ 40 m. This is because the torque from the output shaft of the gear motor is transmitted to the actuators of each bay via the drive shaft; as the length of the drive shaft increases, the load driven by the entire system increases linearly with the length. The longer the shaft, the greater the cumulative torsional angle difference between the output end and the terminal end, which in turn causes the action of the terminal actuator to lag behind the output end. This lag leads to asymmetric loads on the greenhouse roof structure and results in asynchronous operation of the system. A layout diagram of a partial elevating system is shown in Figure 3.

2.2.2. Design of the Self-Locking Mechanism

Principle: The self-locking mechanism of the Elevating Greenhouse system is a core transmission component for achieving the smooth elevation of the roof. Its design must meet requirements such as reliable power transmission, safe reverse self-locking, and strong environmental adaptability. The basic working principle of this mechanism is as follows: The gear motor provides input power, which is transmitted to the drive shaft via a gear train to drive the self-locking mechanism to rotate forward and reverse. This rotation further enables the elevation of the roof through the winding and unwinding of the stainless steel wire rope; when power stops or a reverse load exists, the ratchet-pawl mechanism integrated within the self-locking mechanism enables bidirectional mechanical self-locking to prevent the roof from sliding down accidentally, ensuring system safety.

The system primarily consists of a drive shaft, gear components, deflector pulleys, and stainless steel wire ropes (specification: 4 mm, 6 × 7 + 1WS construction, material: 316 stainless steel), among other components. The overall structure is shown in Figure 4. The core design emphasis lies in the matching of transmission and self-locking capabilities. The system’s load mainly originates from the dead weight of the roof (including covering materials). This load is converted into radial tensile force on the self-locking mechanism via the wire ropes, ultimately generating torque that resists reverse rotation of the drive shaft. Second, as a load-bearing component, the stainless steel wire rope’s breaking load must be significantly greater than the working tension to ensure an adequate safety margin. The self-locking mechanism serves as both the power output and self-locking actuation unit, with its internal ratchet-pawl mechanism being the key to realizing the safety function. When the drive shaft rotates forward, the pawl slides over the ratchet teeth, allowing the winding and unwinding of the stainless steel wire rope; when it rotates in reverse, the pawl locks into the ratchet tooth grooves, preventing the roof from sliding down due to gravity or external forces and ensuring the mechanical safety and stability of the mechanism. The drive shaft adopts a hollow structure design to balance lightweight properties and torsional stiffness. The gear set consists of standard involute cylindrical gears (module m = 2, number of teeth z = 31), which are responsible for transmitting and amplifying the motor torque, and their strength must meet the maximum load requirements during the elevation process.

Mechanical analysis: following the aforementioned principle, the specific parameter design is as follows: The selected stainless steel wire rope has a 4 mm specification, a 6 × 7 + 1WS construction, and 316 material, with a minimum breaking load of 8.9 kN [33]. This design adopts bilateral vertical elevating: each standard unit (6 m span, 4 m bay width) is equipped with one set of wire ropes, and each set enables simultaneous elevating on both sides with 2 elevating nodes. The dead weight of the roof for each standard unit is approximately 55 kg (including the steel structure, film, sunshade net, sliding elevating system, and metal accessories). The formula for calculating the maximum tension of the wire rope is:

$$F_{\mathrm{m}}={\displaystyle \frac{W·k}{n}}={\displaystyle \frac{55\times 10}{2}}\times 1.5=412.5N$$

(1)

where $W$ is the gravity of the roof; $k$ is the safety factor, taken as 1.5; $n$ is the number of elevating points, taken as 2.

Therefore, the formula for calculating the actual safety factor of the stainless steel wire rope is:

$$S={\displaystyle \frac{F}{F_m}}={\displaystyle \frac{8.9\times 1000}{412.5}}=21.6$$

(2)

This value meets the safety factor requirement of 8–10 for general engineering standards [34], and also satisfies the requirements for strength and safety factor.

To ensure the accurate realization of the designed travel of the roof and its synchronous control, it is necessary to calculate the capacity of the wire rope of the self-locking mechanism under single-layer winding. The calculation parameters are as follows: hub diameter of the drum $d=25\mathrm{mm}$, diameter of the rope winding disk $L=100\mathrm{mm}$, diameter of the wire rope $d_s=4\mathrm{mm}$, and the number of single-layer winding turns:

$$N={\displaystyle \frac{L-d}{d_s}}={\displaystyle \frac{100-25}{4}}=18$$

(3)

Since the wire rope is closely arranged and wound, its winding diameter increases linearly with the number of turns. The calculation formulas for the centerline diameter $D_n$ of the nth turn of the wire rope and the length $C_n$ of this turn are as follows:

$$D_n=d+n\times d_s$$

(4)

$$C_n=\pi \times D_n$$

(5)

Perform turn-by-turn calculations for $n=1~18$, and summarize the data for the key points in

Table 3. Key Data on Turn-by-Turn Winding Length of Stainless Steel Wire Rope.

Number of Turns	Centerline Diameter (mm)	Length per Turn (m)	Cumulative Length (m)
1 (First Turn)	29	0.091	0.091
9 (Middle Turn)	61	0.192	1.272
18 (Last Turn)	97	0.305	3.562

.

After summing up the lengths of all turns through calculation, the total length of the stainless steel wire rope, denoted as $L_t={\sum C}_n\approx 3.562m$. This length is greater than the requirement for the roof’s descending travel of 2.725 m, and the maximum number of winding and unwinding turns during the actual elevation process is 16 turns.

2.2.3. Design of the Sliding Elevating Device

Principle: The Sliding Elevating Device is the core actuator of the greenhouse elevating system, whose function is to convert the thrust generated by the gear motor into the linear vertical motion of the greenhouse roof. Based on the principle of linear sliding bearings, the core of this device’s design lies in achieving bidirectional sliding with low friction and high stability.

Its operation process is as follows: When the gear motor is activated, it applies horizontal thrust to the central slider of the Sliding Elevating Device via a stainless steel wire rope. This thrust first overcomes the static friction generated by the rubber-coated bearings and plastic-coated nylon double bearings, and then drives the central slider to move at a constant speed along the connecting splints fixed on the greenhouse columns. During this process, the rubber layer on the outer ring of the rubber-coated bearings effectively absorbs vibrations and disperses contact stress through elastic deformation, thereby significantly reducing dry friction between metals; meanwhile, the nylon double bearings with self-lubrication ensure the accuracy of the sliding direction and maintain long-term operational stability under lubrication-free conditions. Together, the two types of bearings ensure low wear and high synchronicity during the sliding elevation process.

System Parameter Selection: Based on the aforementioned operating principle, the Sliding Elevating Device is specifically composed of connecting splints, rubber-coated bearings, plastic-coated nylon double bearings, and a central slider. Its key design and selection parameters are as follows (overall structure shown in Figure 5): The connecting splints are made of hot-dip galvanized steel sheets (thickness δ = 2 mm), whose function is to firmly integrate the Sliding Elevating Device into the main structure of the greenhouse and achieve a rigid connection with the columns via M8 bolts, thereby ensuring the effective transmission of elevating loads. The rubber-coated bearings (model: φ 40 × 11 − M8) feature a rubber-coated outer ring and a metal inner ring. Installed in the pre-drilled holes of the connecting splints, their main function is to reduce frictional resistance with the central slider through the elastic deformation of rubber, and achieve vibration-damping and buffering effects. The plastic-coated nylon double bearings (model: φ 30 × 50 − M8) have inner and outer rings injection-molded from nylon, featuring self-lubrication and high weather resistance (applicable temperature range: −20 °C to 80 °C). Their core function is to accurately support and guide the movement of the central slider. Additionally, the surface of the guide rail where the central slider contacts the bearings is precision-machined to further reduce friction.

In order to quantitatively evaluate the operating efficiency and reliability of the Sliding Elevating Device, this study conducted an on-site friction force test. Six key nodes were selected in the front, middle, and rear sections along the length of the greenhouse (see Figure 6 for the test site and node layout). A digital display tension meter was used to measure the tension force when driving the roof unit (6 m span, 4 m bay width, self-weight $\mathit{W}=55 \mathrm{kg} \times 10 \mathrm{m}/{\mathrm{s}}^{\mathrm{2}}=550 \mathrm{N}$) for uniform elevating and lowering, and 6 sets of valid data were obtained. The calculation formula for the sliding friction coefficient is as follows:

$$\mathsf{\mu }={\displaystyle \frac{\overline{{\mathrm{F}}_{\mathrm{f}}}}{\mathrm{W}}}$$

(6)

where $\overline{F_f}$ denotes the measured average friction force. The statistics of friction forces at each node and the calculated friction coefficients are shown in

Table 4. Statistics of Friction Forces and Calculated Friction Coefficients at Each Node.

Node Number	Average Friction Force (N)	Friction Coefficient
Node 1	48.25	0.088
Node 2	47.78	0.087
Node 3	9.33	0.017
Node 4	15.37	0.028
Node 5	13.65	0.025
Node 6	18.60	0.034
Overall Average	25.50	0.046

below:

The friction coefficients of Node 1 and Node 2 ($\mathit{\mu }\approx 0.088$) are significantly higher than those of other nodes. This may be attributed to potential issues during installation or manufacturing, such as track installation deviations and bearing seizing, which are indicative of an atypical state. In contrast, the friction coefficients of Nodes 3 to 6 are stable within an extremely low range of 0.017 to 0.034, with an average friction coefficient of only 0.026. This value is far lower than the common friction coefficients of ordinary sliding bearings (usually > 0.1) or bolt-connected nodes. After eliminating individual, correctable installation deviations, the Sliding Elevating Device exhibits stable operating friction, which fully verifies the effectiveness of the combined scheme in this design: “rubber-coated bearings for vibration and resistance reduction + plastic-coated nylon double bearings for low-friction and self-lubrication”. This design meets the operating requirements for the stable and reliable elevation of the greenhouse roof.

Design of Connection Nodes Between the Sliding Elevating Device and Greenhouse Columns: The Sliding Elevating Device is securely attached to the main structure of the greenhouse through a critical connection node, which effectively transfers the elevating load to the columns and arch poles (see Figure 7 for the structural diagram). This node comprises the following components: The connecting splints are made of hot-dip galvanized steel plates (δ = 2 mm) and rigidly connected to the columns using hot-dip galvanized M8 × 60 bolts; Clamping grooves—Fabricated from aluminum alloy profile (6063-T5), these are attached to the arch bars via hot-dip galvanized M6 U-bolts and hoop kits, serving to fix the covering film and internal sunshade system. Limiting angle steels-Hot-dip galvanized ∠30 × 3 angle steel pieces, fixed to the columns with M6 × 30 bolts and eye nuts. Their function is to limit the lateral displacement of the Sliding Elevating Device (designated limit: ±5 mm), thereby preventing deviation during the lifting process. The stainless steel wire rope is anchored to the connecting splints and secured at the ends with wire rope clamps.

2.3. Load Calculation

2.3.1. Calculation of Load Standard Values

The standard values of permanent load, live load, and wind load are calculated, respectively, as follows:

(1)

Standard value of permanent load: 0.03 kN/m² (mainly the self-weight of the steel framework).

(2)

Standard value of live load: 0.15 kN/m² (This greenhouse is designed for year-round vegetable production in Hainan, with leafy vegetables as the cultivation target; the suspended weight of crops is not considered).

(3)

Standard value of wind load: The standard value of wind load perpendicular to the greenhouse surface shall be calculated in accordance with the formula specified in the Chinese National Recommended Standard Code for Loads on Agricultural Greenhouse Structures (GB/T 51183-2016) [35] as follows:

$${\omega }_{\mathit{k}}={\omega }_0{\mathit{\mu }}_{\mathit{z}}{\mathit{\mu }}_{\mathit{s}}$$

(7)

where

• ${\omega }_k$—standard value of wind load (kN/m²);
• ${\omega }_0$—basic wind pressure (kN/m²);
• ${\mu }_z$—height variation coefficient of wind pressure;
• ${\mu }_s$—shape coefficient of wind load.

Prior to the calculation, the basic wind pressure (${\omega }_0$) is derived from the fundamental wind speed–pressure relationship, as per the Chinese load code GB 50009-2012 [36], using the formula:

$${\omega }_0={\displaystyle \frac{1}{2}}\rho v^2$$

(8)

where the air density (ρ) is taken as 1.25 kg/m³. This allows for the conversion between wind speed (v) in m/s and wind pressure (ω₀) in kN/m². For reference, key conversions based on the Beaufort wind scale are summarized in

Table 5. Conversion between Wind Speed and Basic Wind Pressure.

Beaufort Scale	Wind Speed Range (m/s)	Calculated Basic Wind Pressure (kN/m2)	Corresponding Condition
9 (Strong Gale)	48.25	≈0.45	Roof Raised
12+ (Typhoon)	47.78	1.30 (Code Stipulated)	Roof Lowered

below.

This study considers two types of operating conditions for the greenhouse roof: the raised state and the lowered state.

Condition 1 (Greenhouse Roof in the Raised State): This condition simulates the scenario of strong winds (e.g., a Level 9 wind) during daily production. The basic wind pressure ${\omega }_0$ is taken as 0.45 kN/m² (approximately the initial wind speed of a Level 9 wind, equivalent to 20.8–24.4 m/s per the Beaufort wind scale). The ground roughness category is Class B, and the structural calculation height is calculated as $3+1.2/2=3.6m$; thus, the wind pressure height variation coefficient ${\mu }_z$ is taken as 0.76. The wind load shape coefficient ${\mu }_s$ is determined in accordance with the provisions for open-type structures in GB/T 51183-2016 (Chinese National Recommended Standard) [35]: ${\mu }_s=-0.75$ for the roof surface [37], ${\mu }_s=+0.8$ for the windward surface, and ${\mu }_s=-0.50$ for the leeward surface [35]. Then:

• Wind load on the roof surface:

$${\omega }_k={\omega }_0{\mu }_z{\mu }_s=0.45 \times 0.76 \times (-0.75)=-0.257 \mathrm{kN}/m^2$$

(9)

2.

Wind load on the windward surface:

$${\omega }_k={\omega }_0{\mu }_z{\mu }_s=0.45 \times 0.76 \times 0.80=0.274 \mathrm{kN}/m^2$$

(10)

3.

Wind load on the leeward surface:

$${\omega }_k={\omega }_0{\mu }_z{\mu }_s=0.45 \times 0.76 \times (-0.50)=-0.171 \mathrm{kN}/m^2$$

(11)

Condition 2 (Roof in the Lowered State): This condition simulates the situation after disaster-prevention measures have been taken for the roof in response to extreme typhoon conditions. In accordance with GB/T 51183-2016 [35], the maximum basic wind pressure with a 20-year return period in Hainan, China (Sanya region) is taken as ${\omega }_0=1.30 \mathrm{kN}/m^2$. The purpose of selecting this extreme wind load is to rigorously verify the ultimate wind resistance performance of the greenhouse structure in its disaster prevention mode. The ground roughness category is Class B. The structural calculation height is $0.275+1.2/2=0.875 m$, and the wind pressure height variation coefficient ${\mu }_z$ is taken as 0.70 [35]. Then:

1.

Wind load on the roof surface:

$${\omega }_k={\omega }_0{\mu }_z{\mu }_s=1.30 \times 0.70 \times (-0.75)=-0.683 \mathrm{kN}/m^2$$

(12)

2.

Wind load on the windward surface:

$${\omega }_k={\omega }_0{\mu }_z{\mu }_s=1.30 \times 0.70 \times 0.80=0.728 \mathrm{kN}/m^2$$

(13)

3.

Wind load on the leeward surface:

$${\omega }_k={\omega }_0{\mu }_z{\mu }_s=1.30 \times 0.70 \times (-0.50)=-0.455 \mathrm{kN}/m^2$$

(14)

2.3.2. Calculation of Load Design Values

The acting loads mainly include permanent loads, live loads, and wind loads, with wind load being the dominant load. The design values of the loads are calculated based on the design value of the effect controlled by variable loads $S_d$ and relevant calculation methods. In accordance with the provisions of the Chinese Code for Loads on Agricultural Greenhouse Structures (GB/T 51183-2016) [35], the calculation formula is as follows:

$$S_d={\mathit{Y}}_0({\mathit{Y}}_G{S}_{\mathit{Gk}}+{\mathit{Y}}_{Q1}{S}_{Q1k}+\sum _{\mathit{i}\mathit{=}2}^{\mathit{n}}{\mathit{Y}}_{\mathit{Qi}}{\Psi }_{\mathit{Ci}}{S}_{\mathit{Qik}})$$

(15)

where

• $S_d$—design value of load effect;
• ${\mathit{Y}}_0$—structural importance factor, taken as 0.9;
• ${\mathit{Y}}_G$—partial factor for permanent load, taken as 1.0;
• ${\mathit{Y}}_{Q1}$,${\mathit{Y}}_{\mathit{Qi}}$—denote the partial factors for the 1st and ith variable loads, respectively, where ${\mathit{Y}}_{Q1}$ (for wind load) is taken as 1.0 and ${\mathit{Y}}_{\mathit{Qi}}$ (for live load) is taken as 1.2;
• ${\Psi }_{\mathit{Ci}}$—combination value factor for live load, taken as 0.7;
• $S_{\mathit{Gk}}$, $S_{\mathit{Qik}}$, $S_{\mathit{Q}1\mathit{k}}$—load effects caused by the standard value of permanent load, the standard value of live load (where n = 2), and the standard value of wind load, respectively.

The span $L$ of the greenhouse is 4.0 m. The calculated values of each load are as follows:

1

Design value of permanent load:

$${\mathit{Y}}_0{\mathit{Y}}_{\mathit{G}}{S}_{\mathit{Gk}}L=0.9 \times 1.0 \times 0.03 \mathrm{kN}/m^2\times 4.0 m=0.108 \mathrm{kN}/m$$

(16)

2

Design value of live load:

$${\mathit{Y}}_0{{\mathit{Y}}_{\mathit{Qi}}\Psi }_{\mathit{Ci}}{S}_{\mathit{Qik}}L=0.9 \times 1.2 \times 0.7 \times 0.15 \mathrm{kN}/m^2\times 4.0 m=0.4536 \mathrm{kN}/m$$

(17)

3

For the design value of wind load, the wind resistance coefficient $\epsilon$ of the 40-mesh insect-proof net (taken as 0.81) [38] shall be considered, and it shall be calculated separately for the two operating conditions:

Condition 1 (Greenhouse Roof in the Raised State):

①

Roof surface:

$${\mathit{Y}}_0{\mathit{Y}}_{Q1}{S}_{Q1k}L=0.9 \times 1.0 \times (-0.253 \mathrm{kN}/m^2)\times 4.0 m=-0.91 \mathrm{kN}/m$$

(18)

②

Windward surface:

$${\mathit{Y}}_0{\mathit{Y}}_{Q1}{S}_{Q1k}L\epsilon =0.9 \times 1.0 \times 0.274 \mathrm{kN}/m^2 \times 4.0m \times 0.81 = 0.80 \mathrm{kN}/m$$

(19)

③

Leeward surface:

$${\mathit{Y}}_0{\mathit{Y}}_{Q1}{S}_{Q1k}L\epsilon =0.9\times 1.0 \times (-0.171\mathrm{kN}/m^2)\times 4.0 m\times 0.81=-0.50\mathrm{kN}/m$$

(20)

Condition 2 (Roof in the Lowered State):

①

Roof surface:

$${\mathit{Y}}_0{\mathit{Y}}_{Q1}{S}_{Q1k}L=0.9\times 1.0 \times (-0.683 \mathrm{kN}/m^2)\times 4.0m=-2.46 \mathrm{kN}/m$$

(21)

②

Windward surface:

$${\mathit{Y}}_0{\mathit{Y}}_{Q1}{S}_{Q1k}L\epsilon =0.9\times 1.0\times 0.728 \mathrm{kN}/m^2\times 4.0m\times 0.81=2.12 \mathrm{kN}/m$$

(22)

③

Leeward surface:

$${\mathit{Y}}_0{\mathit{Y}}_{Q1}{S}_{Q1k}L\epsilon =0.9\times 1.0 \times (-0.455 \mathrm{kN}/m^2)\times 4.0m\times 0.81=-1.33 \mathrm{kN}/m$$

(23)

Table 6. Summary of Load Design Values.

Load Type	Condition 1 (Roof in the Raised State)	Condition 2 (Roof in the Lowered State)	Unit	Remarks
Permanent load	+0.108	+0.108	kN/m	Vertical downward
Live load	+0.4536	+0.4536	kN/m	Vertical downward
Wind load—roof surface	−0.91	−2.46	kN/m	Suction
Wind load—windward surface	+0.80	+2.12	kN/m	Pressure
Wind load—leeward surface	−0.50	−1.33	kN/m	Suction

Note: “+” indicates pressure (direction toward the component); “−” indicates suction (direction away from the component).

summarizes the calculation results of load design values under the two operating conditions. Among them, the wind load is the dominant load, which will be used for subsequent structural internal force calculations and component design to ensure the greenhouse’s safety during normal service and extreme weather. The load values in Condition 2 are larger, which demonstrates the effectiveness of roof lowering as a disaster-prevention measure, while also imposing higher requirements on structural strength.

2.4. Structural Calculations

In structural design, the stress ratio is a crucial indicator for evaluating the safety level of components. It is defined as the ratio of a component’s design stress under loads to its ultimate stress (i.e., the maximum stress the component can withstand, corresponding to its design bearing capacity). The relationship between this ratio and 1.0 directly determines the safety of the component [39]: If the stress ratio is less than 1.0, it indicates that the design stress of the component is lower than its bearing capacity, and the component meets safety requirements—with a smaller ratio corresponding to a larger safety margin; if the stress ratio is equal to 1.0, it represents the theoretical limit state, indicating that the design stress of the component exactly equals its bearing capacity; if the stress ratio is greater than 1.0, it indicates that the design stress of the component has exceeded its bearing capacity, the component is in an unsafe state, and the design fails to meet Chinese codes requirements. In this study, the stress ratios are specifically categorized into three types: Strength stress ratio: It refers to the ratio of the maximum stress on a component’s cross-section (e.g., the combined stress due to axial force and bending moment) to the design value of the material strength (e.g., the yield strength of steel). It is used to verify whether the cross-sectional strength is sufficient to prevent failure due to yielding or fracture. A strength stress ratio less than 1.0 indicates that the cross-sectional strength is adequate. In-plane stability stress ratio: It primarily refers to the verification of the bearing capacity against buckling for compression members within the plane of bending moment action. An in-plane stability stress ratio less than 1.0 indicates that the member will not experience buckling within the plane of bending moment. Out-of-plane stability stress ratio: It refers to the verification of the bearing capacity against buckling for compression members in the direction perpendicular to the plane of bending moment action. When a member is bent in-plane, insufficient lateral bracing may lead to flexural–torsional buckling out of the plane. An out-of-plane stability stress ratio less than 1.0 indicates that the member will not undergo lateral instability.

Mechanical Model Construction

The PKPM 2010 structural calculation software was used to conduct internal force analysis and member verification for the Elevating Greenhouse under two states: roof raised (Condition 1) and roof lowered (Condition 2). The calculation model accurately accounted for all loads and their combinations as specified in the aforementioned load calculation. The results are presented in the form of stress ratio diagrams (see Figure 8 and Figure 9). The number on the left represents the strength stress ratio, the number in the upper right corner represents the in-plane stability stress ratio, and the number in the lower right corner represents the out-of-plane stability stress ratio. The maximum stress ratio results of the key members are summarized in

Table 7. Maximum Stress Ratios of Key Components of the Elevating Greenhouse.

Component Name	Cross-Sectional Dimension (mm)	Working Condition	Strength Stress Ratio	In-Plane Stress Ratio	Out-of-Plane Stress Ratio
Column	Rectangular tube ☐ 80×40×1.5	Roof Raised	0.96	0.68	0.43
		Roof Lowered	0.90	0.36	0.27
External Sunshade Column	Rectangular tube ☐ 80 × 40 × 1.5	Roof Raised	0.29	0.29	0.11
		Roof Lowered	0.03	0.02	0.02
Horizontal Tie Rod	Circular tube φ 32 × 1.6	Roof Raised	0.91	0.90	0.90
		Roof Lowered	0.25	0.30	0.30
Web Member	Circular tube φ 25 × 1.5	Roof Raised	0.02	0.09	0.09
		Roof Lowered	0.02	0.09	0.09
Arch Bar	Circular tube φ 32 × 1.6	Roof Raised	0.49	0.52	0.52
		Roof Lowered	0.94	0.52	0.52
External Sunshade Beam	Rectangular tube ☐ 50 × 50 × 2	Roof Raised	0.14	0.15	0.05
		Roof Lowered	0.04	0.04	0.03
External Sunshade Diagonal Brace	Circular tube φ 25 × 1.5	Roof Raised	0.03	0.13	0.13
		Roof Lowered	0.01	0.04	0.04

.

3. Results

Through the analysis of the stress ratio calculation results for the key components of the Elevating Greenhouse under two working conditions (as presented in Table 7), it is found that the strength stress ratios and stability stress ratios of all components are less than 1.0 [39]. This indicates that under the design load, the structure not only meets the strength requirements for each cross-section, but also the compression members maintain stability in both in-plane and out-of-plane directions. The structure complies with the strength and stability requirements specified in the Chinese National Standard Design Standard for Agricultural Greenhouse Structures (GB/T 51424-2022) [29] and the Chinese National Standard Code for Design of Steel Structures (GB 50017-2017) [39], confirming its overall safety and reliability. However, there are significant differences in the stress distribution among different components:

Under the roof-lowered condition (extreme wind load), the Arch Bar has a strength stress ratio of 0.94 (close to the code limit of 1.0), ensuring the roof remains intact during severe typhoons and protecting internal leafy vegetables from wind damage. This indicates that the Arch Bar is a key safety component of the structure under extreme wind load conditions, and the material strength is fully utilized. As the main vertical load—bearing component, the Column has relatively high strength stress ratios under both working conditions (0.96 in the roof—raised condition and 0.90 in the roof—lowered condition), indicating a stable stress state. In the roof—raised condition, both the strength stress ratio and stability stress ratio of the Horizontal Tie Rod are at high levels (0.91 and 0.90, respectively), which shows that the bearing capacity of this component is fully exerted. In contrast, the stress ratios of secondary components such as the External Sunshade Columns, External Sunshade Beams, and External Sunshade Diagonal Braces are generally low (all strength stress ratios are less than 0.30). This indicates that their cross—sectional dimensions are controlled by stability or structural requirements, and they also serve as a reserve for the horizontal loads generated during the horizontal operation of the electric sunshade system.

In terms of the relationship between stability and strength, for components such as Web Members and Arch Bars, their in-plane and out-of-plane stability stress ratios are equal and higher than their strength stress ratios. This indicates that their in-plane and out-of-plane stable bearing capacities are the same, and the components have achieved a stable equal-strength design, realizing the balance of bidirectional stability. Thus, the design is economically reasonable.

3.1. Mechanical Analysis of Key Components

To comprehensively investigate the mechanical performance of the key structural components, three types of components subjected to the most critical stresses were selected for in-depth comparative analysis based on the aforementioned stress ratio results: the Column (with the highest strength stress ratio of 0.96), the Horizontal Tie Rod (with the highest stability stress ratio of 0.90), and the Arch Bar (the member with the maximum displacement deformation). The detailed internal forces and stresses calculated using PKPM 2010 software are compared for these three component types in

Table 8. Analysis Results of Mechanical Performance for Key Components.

Component Name	Working Condition	Max. Strength Stress (N/mm2)	Max. In-Plane Stress (N/mm2)	Max. Out-of-Plane Stress (N/mm2)	Slenderness Ratio	Axial Force (kN)	Bending Moment (kN·m)
Column	Roof Raised	197.0	139.4	83.6	95	−2.50	−0.45
	Roof Lowered	184.5	104.5	62.7	95	−2.10	−0.35
Arch Bar	Roof Raised	36.8	6.72	4.99	65	−0.21	−0.32
	Roof Lowered	193.0	8.45	6.45	187	0.09	0.01
Horizontal Tie Rod	Roof Raised	186.6	185.0	185.0	180	−1.10	−0.15
	Roof Lowered	51.3	61.5	61.5	180	−0.25	−0.03

.

As can be seen from Table 8, The Column is the component governing the structural strength. Under the raised condition, its maximum stress is relatively high, which is jointly caused by the considerable axial force and bending moment it bears as the main vertical load-bearing component. Its design is therefore controlled by strength. The Horizontal Tie Rod is controlled by stability: This component exhibits high in-plane and out-of-plane stability stresses under the raised condition, which are very close to its strength stress. This indicates that its load-bearing capacity is not determined by material strength but is governed by stability. The Arch Bar is also a strength-controlled component: Under the lowered condition, its strength stress is second only to that of the Column. Consequently, the Arch Bar is a key load-transferring component within the structural system, and its safety is crucial under extreme working conditions.

3.2. Displacement Analysis

For the steel frame of the greenhouse, which bears loads, the stress stability of each component is a key indicator in design. The stress of each component must be less than the design strength of Q235 cold-formed thin-walled steel (205 N/mm²) [40]. This study analyzed the displacement response of the Elevating Greenhouse roof under the two working conditions: roof raised and roof lowered. After applying the corresponding constraints and loads, the overall displacement and strain diagram of the steel structure is shown in Figure 10.

Analysis of Figure 10 shows that under wind load, the maximum node displacement in both working conditions occurs at the joint between the arch frame and Web Members. In the roof-raised condition, the maximum horizontal displacement d_x of the node is 36.3 mm; in the roof-lowered condition, the maximum vertical displacement d_y of the node is 4.9 mm. Displacements in the edge areas and near the supports are relatively small. The deformation displacement of the steel structure meets the deformation requirements, as specified in the current Chinese National Standard Design Standard for Agricultural Greenhouse Structures (GB/T 51424-2022) [29]: the maximum displacement of the greenhouse structure under the combination of characteristic load values shall be controlled between 1/60 and 1/180 of the greenhouse span. Referring to this standard, the maximum displacement limit in this study is set to 1/60 of the span (i.e., approximately 1.6%), calculated as follows: $\mathbf{6000} \mathbf{mm} \times \mathbf{1.6}\mathbf{\%} \mathbf{=} \mathbf{96} \mathbf{mm}$ [29]. Thus, the deformation requirements are satisfied. In addition, a comparison of the two working conditions reveals that the displacement values of all components in the roof-lowered condition are significantly reduced. This indicates that when a typhoon occurs, lowering the roof to the ground can effectively reduce structural response, minimize the risk of greenhouse damage, and thereby reduce economic losses.

3.3. Comparative Analysis

The Elevating Greenhouse was compared with the ordinary circular-arch greenhouse of the same function in Hainan, China (with the same span, bay width, arch spacing, eave height, and design wind load).

3.3.1. Stress Analysis

For the ordinary circular-arch greenhouse, the characteristic values and design values of permanent loads and live loads are consistent with those of the Elevating Greenhouse. The basic wind pressure ${\omega }_0$ is set to 1.30 kN/m², which is the same as the value adopted for the Elevating Greenhouse in the roof-lowered state. The PKPM 2010 structural calculation software was used to conduct internal force analysis and member verification for the ordinary circular-arch greenhouse structure. All selected member specifications passed the calculation verification, and the calculation results are presented in the form of stress ratio diagrams (see Figure 11). The maximum stress ratio results of key members are summarized in

Table 9. Stress Ratio Distribution of Key Components of the Ordinary Circular-arch Greenhouse.

Component Name	Cross-Sectional Dimension (mm)	Strength Stress Ratio	In-Plane Stress Ratio	Out-of-Plane Stress Ratio
Column	Rectangular tube ☐ 120 × 50 × 3	0.90	0.06	0.06
External Sunshade Column	Rectangular tube ☐ 50 × 50 × 2	0.30	0.30	0.11
Horizontal Tie Rod	Circular tube φ 40 × 1.5	0.26	0.75	0.75
Web Member	Circular tube φ 25 × 1.5	0.02	0.09	0.09
Arch Bar	Circular tube φ 40 × 1.5	0.71	0.35	0.35
External Sunshade Beam	Rectangular tube ☐ 50 × 50 × 2	0.17	0.18	0.16
External Sunshade Diagonal Brace	Circular tube φ 25 × 1.5	0.03	0.14	0.14

.

As can be seen from Figure 11 and Table 9, the strength stress ratios and stability stress ratios of all components are far less than 1.0. Under the design load, the structure meets the requirements of relevant Chinese codes and is safe and reliable overall. However, there are significant differences in the stress state and safety reserve among different components, with specific analysis as follows: The strength stress ratio of the Column is as high as 0.90, indicating that its material strength has been fully utilized, and it is the most critical load-bearing component in the entire structural system. Although its stability stress ratio is low (0.06), it shows that the Column has effective lateral constraints in both in-plane and out-of-plane directions, with sufficient stability reserve. The Horizontal Tie Rod has a relatively low strength stress ratio (0.26) but a relatively high stability stress ratio (0.75), which indicates that the section selection of this component is mainly controlled by stability requirements. Both the strength stress ratios and stability stress ratios of the Arch Bars and Web Members are at a low level (below 0.35), with the strength stress ratios higher than the stability stress ratios. This shows that these two types of components have achieved the optimal balance between strength and stability, with balanced material utilization, making them the most economical and effective part of the structure.

3.3.2. Comparative Analysis of Material Consumption

To conduct a comparative analysis of the material economy of the Elevating Greenhouse designed in this paper, the material specifications of the main components of the Elevating Greenhouse were compared with those of the ordinary circular-arch greenhouse. Quantitative comparative analysis was performed by calculating the steel consumption of the main frame structural components of a single-unit frame (with a 6 m span). All components were calculated based on Q235 steel, and the steel density $\rho$ was set to 7850 kg/m³ [39]. The formula for calculating the unit-length weight $w$ of components of each specification is as follows:

$$\mathrm{Rectangular} \mathrm{tube}:w=2·t·(h+b-2t)·\rho$$

(24)

$$\mathrm{Circular} \mathrm{tube}:w=\pi ·t(D-t)·\rho$$

(25)

where $h$ is the section height (m); $b$ is the section width (m); $D$ is the outer diameter of the pipe (m); $t$is the wall thickness (m).

The specifications of the main components of the two types of greenhouses and the unit-length mass calculated using the above formula are presented in

Table 10. Main Component Specifications of the Elevating Greenhouse and Ordinary Circular-arch Greenhouse.

Component Name	Greenhouse Type	Cross-Sectional Dimension (mm)	Unit-Length Mass (kg/m)
Column	Elevating Greenhouse	Rectangular tube ☐ 80 × 40 × 1.5	2.755
	Ordinary Greenhouse	Rectangular tube ☐ 120 × 50 × 3	8.195
External Sunshade Column	Elevating Greenhouse	Rectangular tube ☐ 80 × 40 × 1.5	2.755
	Ordinary Greenhouse	Rectangular tube ☐ 50 × 50 × 2	3.014
Horizontal Tie Rod	Elevating Greenhouse	Circular tube φ 32 × 1.6	1.200
	Ordinary Greenhouse	Circular tube φ 40 × 1.5	1.424
Web Member	Elevating Greenhouse	Circular tube φ 25 × 1.5	0.869
	Ordinary Greenhouse	Circular tube φ 25 × 1.5	0.869
Arch Bar	Elevating Greenhouse	Circular tube φ 32 × 1.6	1.200
	Ordinary Greenhouse	Circular tube φ 40 × 1.5	1.424
External Sunshade Beam	Elevating Greenhouse	Rectangular tube ☐ 50 × 50 × 2	3.014
	Ordinary Greenhouse	Rectangular tube ☐ 50 × 50 × 2	3.014
External Sunshade Diagonal Brace	Elevating Greenhouse	Circular tube φ 25 × 1.5	0.869
	Ordinary Greenhouse	Circular tube φ 25 × 1.5	0.869

.

Taking a single-span single-arch frame (with a 6 m span) as the calculation unit, the steel consumption of each component and the total steel consumption for the two types of greenhouses are presented in

Table 11. Steel Consumption of Components for the Standard Single-Span Frame (6 m Span) of Two Greenhouse Types.

Component Name	Length (m)	Quantity	Steel Consumption (kg)
			Elevating Greenhouse	Ordinary Greenhouse
Column	3.00	2	16.53	49.17
External Sunshade Column	1.50	2	8.27	9.04
Horizontal Tie Rod	6.00	1	7.20	8.54
Arch Bar	8.00	1	6.95	6.95
External Sunshade Beam	6.45	1	7.74	9.18
External Sunshade Diagonal Brace	6.00	1	18.08	18.08
Total			67.38	103.58

. The formula for calculating the total steel ${\mathit{W}}_t$ consumption is as follows:

$${\mathit{W}}_t=\sum (L\times w_i)$$

(26)

where $L$ is the total length of the component (m); $w_i$ is the corresponding unit-length mass of the component (kg/m).

The calculation results show that the steel consumption of one unit frame of the Elevating Greenhouse designed in this paper is 67.38 kg, while that of the comparative ordinary circular-arch greenhouse unit frame is 103.58 kg. The Elevating Greenhouse achieves a weight reduction of 36.20 kg, with a weight reduction ratio of 35%. Comparing the data of each component, the most significant weight reduction is observed in the greenhouse columns: the steel consumption of the columns in the Elevating Greenhouse is 16.53 kg, whereas that in the ordinary greenhouse is 49.17 kg. This single component alone achieves a weight reduction of 32.64 kg, accounting for 90.2% of the total weight reduction. Next, both the arch bars and horizontal tie rods also achieve weight reduction due to the reduced height, which decreases the wind pressure height variation coefficient. The combined weight reduction in these two components is approximately 2.78 kg. In summary, compared with the traditional ordinary circular-arch greenhouse, the unit frame of the Elevating Greenhouse reduces material consumption by more than one-third, achieving a lightweight design and efficient material utilization. While saving materials, it also facilitates transportation and installation, demonstrating the rational structure and economic feasibility of this design.

4. Discussion

Through design and engineering verification, this study not only proves the technical feasibility of the Elevating Greenhouse but also inspires reflections on the design concept and engineering implementation. The specific discussion is as follows:

(1) This study achieves the transformation of the design paradigm from traditional “passive resistance” to “active adaptation”. The PKPM analysis results (stress ratio < 1.0) confirm the structural safety, but its in-depth value lies in revealing the realization path of structural lightweighting: the improvement of wind resistance after the roof is lowered mainly stems not from the surplus of material strength, but from the dynamic adjustment of the building form to reduce the wind load effect. Calculations show that even when the design value of wind load increases significantly after the roof is lowered, the structural response can still remain within the safe range. This confirms the effectiveness of the “replacing materials with mechanisms” strategy from the mechanical perspective.

(2) In contrast to existing technologies, including research from China, the Netherlands, and Japan, which primarily follow a “passive resistance” strategy focusing on optimizing structural parameters and developing new greenhouse morphologies—approaches that, while improving performance, remain static after construction and ultimately rely on increasing material stiffness and strength to resist loads—this study proposes a paradigm shift towards “active adaptation.” It adopts an innovative strategy for the mechanism implementation path: employing a mechatronic steel cable synchronous elevation system. This system can actively and rapidly alter the structural configuration based on disaster warnings to withstand wind loads. While this approach imposes higher demands on driving and control, it offers clear structural force transmission, precise synchronous control, and adaptability to large-area driving, making it more suitable for large-scale, standardized modern agricultural production scenarios.

(3) In the design of the key elevating mechanism, the mechanical self-locking of the ratchet-pawl, the low-friction Sliding Elevating Device (with a measured friction coefficient μ = 0.017–0.034), and the electrical overload protection together form multiple safety guarantees for the system, providing a safety assurance for the production application of roof elevation.

(4) This study still has certain limitations. While the structural safety and mechanism functionality of the Elevating Greenhouse have been verified, and theoretical synchronization has been ensured through design, the dynamic synchronization accuracy during actual roof elevation operations—specifically, the cooperative performance of multiple sets of steel cables under complex working conditions such as wind disturbances and friction variations—requires further attention. Any asynchrony may cause the roof to tilt, leading to increased friction and a risk of jamming in the sliding mechanism. Building on this, future research could integrate environmental sensing and deviation correction control systems to address the synchronization issue during the elevation process. Furthermore, after the greenhouse roof is lowered, the wind load on the roof is relatively large, requiring effective fixation between the roof and the columns to resist these loads. The current solution proposed in this study is manual hook fixation, which has low efficiency. The convenience of use could be significantly enhanced by installing an automatic locking device at the column base.

5. Conclusions

Against the backdrop of the needs of protected agriculture in tropical regions represented by Hainan, China, and targeting the climatic characteristics of frequent typhoons and heavy rainfall in summer and autumn as well as occasional cold waves in winter, this study developed a greenhouse with an elevable roof based on the existing circular-arch greenhouse. Research and Development (R&D) and optimization design were carried out from aspects of structural form, system composition, and key system parameters. Meanwhile, structural calculation and analysis were carried out using the maximum wind load with a 20-year return period in Hainan, China (Sanya region). A comparative analysis was also performed on the structure and material consumption with the ordinary circular-arch greenhouse with a fixed roof under the same parameters. These efforts verified the rationality of the structural parameters and structural economy of the Elevating Greenhouse studied in this paper. The relevant research and design conclusions are as follows:

(1) Strong innovation in structural design: A multi-span greenhouse structure with an elevable roof is proposed. Combined with the mechatronic steel cable elevation system, it realizes the overall synchronous elevation of the roof and possesses the capability to proactively respond to extreme weather. After the roof is lowered, the height of wind load acting on the columns and the wind load shape coefficient of the roof can be significantly reduced, thereby improving the overall wind-resistant stability of the greenhouse.

(2) Safety and reliability of key systems: The elevation system adopts a geared motor for driving and a cable reel-steel cable transmission, combined with thermal relay overload protection, ensuring stable operation and high synchronization. The self-locking mechanism integrates a ratchet-pawl structure, which reliably locks the roof at any position and prevents accidental sliding. The Sliding Elevating Device uses a combination of rubber-coated bearings and nylon double bearings, featuring low friction and ensuring stability during long-term operation.

(3) Stress and displacement analyses were conducted for two typical working conditions (roof raised/lowered) using PKPM software. All component stress ratios are less than 1.0, and the maximum displacement meets the code limits, indicating that the structure is safe and reliable. It complies with the requirements of Chinese standards: Design Standard for Agricultural Greenhouse Structures (GB/T 51424-2022) and Standard for Design of Steel Structures (GB 50017-2017).

(4) Compared with the ordinary circular-arch greenhouse, the total steel consumption of the standard unit steel frame of the Elevating Greenhouse has been reduced from 103.58 kg to 67.38 kg, a decrease of 35%, achieving a steel consumption saving of more than one-third. Among this reduction, the weight of columns accounts for 90.2%, while the combined weight reduction in arch bars and horizontal tie rods is 2.79 kg. This realizes the lightweight design and efficient utilization of greenhouse structural materials.

The typhoon-resistant multi-span greenhouse with an elevable roof proposed in this study demonstrates comprehensive advantages in structural innovation, system safety, economy, and functionality. This Elevating Greenhouse provides effective technical support for disaster-resilient and sustainable protected agriculture in tropical regions, aligning with global goals of food security under climate change, and has high promotion potential.