Search Results (153)

Preventing progressive collapse induced by accidental events poses a critical challenge in the design and construction of resilient structures. While substantial progress has been made in planar structures, the progressive collapse mechanisms of precast concrete spatial structures—particularly regarding the effects of precast slabs—remain inadequately explored. This study develops a refined finite element modeling approach to investigate progressive collapse mechanisms in fully bonded prestressed precast concrete (FB-PPC) spatial frames, both with and without precast slabs. The modeling approach was validated against available test data from related sub-assemblies, and applied to assess the collapse performance. A series of pushdown analyses were conducted on the spatial frames under various column removal scenarios. The load–displacement curves, slab contribution, and failure modes under different conditions were compared and analyzed. A simplified energy-based dynamic assessment was additionally employed to offer a rapid estimation of the dynamic collapse capacity. The results show that when interior or side columns fail, the progressive collapse process can be divided into the beam action stage and the catenary action (CA) stage. During the beam action stage, the compressive membrane action (CMA) of the slabs and the compressive arch action (CAA) of the beams work in coordination. Additionally, the tensile membrane action (TMA) of the slabs strengthens the CA in the beams. When the corner columns fail, the collapse stages comprise the beam action stage followed by the collapse stage. Due to insufficient lateral restraints around the failed column, the development of CA is limited. The membrane action of the slabs cannot be fully mobilized. The contribution of the slabs is significant, as it can substantially enhance the vertical resistance and restrain the lateral displacement of the columns. The energy-based dynamic assessment further reveals that FB-PPC spatial frames exhibit high ductility and residual strength following sudden column removal, with dynamic load–displacement curves showing sustained plateaus or gentle slopes across all scenarios. The inclusion of precast slabs consistently enhances both the peak load capacity and the residual resistance in dynamic collapse curves. Full article

The shear tests are conducted on six precast segmental concrete beams (PSCBs) in this paper. A new specimen design scheme is presented to compare the effects of segmental joints on the shear performance of PSCBs. The failure modes, shear strength, structural deflection, stirrup strain, and tendon stress are recorded. The factors of shear span ratio, the position of segmental joints, and hybrid tendon ratio are focused on, and their effects on the shear behaviors are compared. Based on the measured responses, the shear contribution proportions of concrete segments, prestressed tendons, and stirrups are decomposed and quantified. With the observed failure modes, the truss–arch model is employed to clarify the shear mechanism of PSCBs, and simplified equations are further developed for predicting the shear strength. Using the collected test results of 30 specimens, the validity of the proposed equations is verified with a mean ratio of calculated-to-test values of 0.96 and a standard deviation of 0.11. Furthermore, the influence mechanism of shear span ratio, segmental joints, prestressing force, and hybrid tendon ratio on the shear strength is clarified. The increasing shear span ratio decreases the inclined angle of the arch ribs, thereby reducing the shear resistance contribution of the arch action. The open joints reduce the number of stirrups passing through the diagonal cracks, lowering the shear contribution of the truss action. The prestressing force can reduce the inclination of diagonal cracks, improving the contribution of truss action. The external unbonded tendon will decrease the height of the arch rib due to the second-order effects, causing lower shear strength than PSCBs with internal tendons. Full article

This study applied precast engineered cementitious composite (ECC) shells to replace conventional concrete in precast assembled monolithic composite beams to enhance mechanical performance. A new type of precast monolithic ECC composite beam was proposed. Five ECC composite beams and one reinforced concrete (RC) composite beam were designed and fabricated for the experimental study. The failure pattern, failure mechanism, load-bearing capacity, deformability, and stiffness degradation were quantitatively analyzed through the tests. The main findings were as follows: ECC composite beams developed finer and more densely distributed cracks compared to RC composite beams, without significant concrete spalling. The peak load of ECC composite beams was 8.2% higher than that of RC composite beams, while the corresponding displacement at peak load increased by 29.3%. The ECC precast shell delayed crack propagation through the fiber bridging effect. The average load degradation coefficient of the ECC composite beams was 8.2% lower than that of the RC beam. The stiffness degradation curve of ECC composite beams was more gradual than that of RC composite beams, providing an optimization basis for the design of precast beams in structures with high seismic demands. As the shear span ratio increased from 1.5 to 3, the load-bearing capacity decreased by 32.0%. When the stirrup ratio increased from 0.25% to 0.75%, the ultimate load-bearing capacity improved by 28.8%. Furthermore, specimens with higher stirrup ratios showed a 40–50% reduction in stiffness degradation rate, demonstrating that increased stirrup ratio effectively mitigated brittle failure. Full article

The pre-inserted method for precast shear walls involves casting concealed beams at floor slabs between upper and lower structures, with precast concrete supports spaced at intervals. Vertical rebars at the base of upper walls are pre-inserted and anchored in the beams before slab casting. It offers advantages such as convenient construction without the need for grouting, demonstrating broad application prospects and significant promotional value. To evaluate seismic performance, quasi-static cyclic loading tests were conducted on five specimens: three full-scale pre-inserted precast walls and two cast-in-place counterparts. Under increasing lateral displacement, low axial-load specimens failed via tensile fracture of the outermost rebars, while high axial-load specimens failed by concrete crushing in compression. The test results showed that under identical axial-load ratios, the precast walls exhibited comparable bearing capacity, stiffness degradation, and energy dissipation to cast-in-place walls, but superior deformation ductility. The ultimate drift ratios of pre-inserted walls exceeded those of cast-in-place walls by 16.7% (axial-load ratio 0.2) and 22.2% (axial-load ratio 0.4), demonstrating robust seismic performance. Full article

Traditional techniques for detecting internal defects in concrete are limited by the weak directivity of ultrasonic waves, significant signal attenuation, and low imaging contrast. This paper presents an improved synthetic aperture focusing technique (SAFT) enhanced by the Delay Multiply and Sum (DMAS) algorithm to address these limitations and improve both the resolution and signal-to-noise ratio. The proposed method sequentially transmits and receives ultrasonic waves through an array of transducers, and applies DMAS-based nonlinear beam-forming to enhance image sharpness and contrast. Its effectiveness was validated through finite element simulations and experimental tests using three precast concrete specimens with artificial defects (specimen size: 240 mm × 300 mm × 100 mm). Compared with the conventional SAFT, the proposed method improves image contrast by approximately 40%, with clearer defect boundaries and a vertical positioning error of less than ±5 mm. This demonstrates the method’s promising potential for practical applications in internal defect visualization of concrete structures. Full article

The eccentrically braced frame (EBF) is a typical structural system used in high-rise buildings. Current related design methods focus on the concrete and steel structures rather than on the complex composite structure. In addition, they tend to overlook the contribution of the energy-dissipation unit and its corresponding additional influence on the structure. In this study, a precast composite EBF structure is selected as a case study, including the partially steel-reinforced concrete (PSRC) beam and the concrete-filled steel tubular (CFST) column. A modified energy-based design method is proposed to leverage the excellent seismic performance of the precast composite EBF structure. The multi-stage energy-dissipation mechanism and the additional influence of the eccentric braces are systematically considered through the energy distribution coefficient and the layout of dampers. A case study of a 12-floor, three-bay precast composite EBF structure is conducted using a series of nonlinear time-history analyses. Critical seismic responses, including the maximum inter-story drift ratio, residual inter-story drift ratio, and peak acceleration, are systematically analyzed to evaluate the effectiveness of the proposed design theory. The distribution coefficient is recommended to range from 0.70 to 0.80 to balance the energy-dissipation contribution between the frame and the eccentric braces. In terms of the damper layout, the energy-dissipation contribution of the eccentric brace should differ among the lower, middle, and upper floors. Full article

The introduction of a novel replaceable plastic hinge technology aims to enhance the performance of precast reinforced concrete (PRC) frames, particularly in seismically vulnerable areas where substandard structural systems are prevalent. This artificially controllable plastic hinge (ACPH) mechanism effectively localizes inelastic deformations to a detachable steel subassembly, thereby maintaining the integrity of the primary structural components. A numerical analysis was carried out on four distinct PRC frame configurations that utilized concrete and steel of inferior quality relative to contemporary standards. The frames underwent testing under a segment of the Mw 7.7 Kahramanmaraş ground motion, revealing that connections utilizing the ACPH not only reduce peak base shear but also mitigate cracking at beam–column interfaces, directing plastic strains towards replaceable fuse elements. The implementation of the ACPH also facilitates extended structural periods and localized plastic hinging, which serves to limit damage to essential members while expediting post-earthquake repairs. Comparative validation through prior subassembly tests confirms that this hinge exhibits a strong hysteretic response and ductile performance, surpassing traditional wet-joint connections in the context of substandard PRC frames. Overall, these results underscore the potential of standardized hinge modules in enhancing seismic resilience and supporting swift, economical rehabilitation of critical infrastructure. Thus, this proposed technology effectively tackles persistent issues related to low-strength materials in precast structures, presenting a practical approach to improving earthquake resilience and minimizing repair time and costs. Full article

To investigate the mechanical behavior of precast columns with openings in the beam–column joint core area under axial loads, a systematic study was conducted to examine the effects of the opening parameters on the axial mechanical performance of precast columns. Two sets of six precast concrete column specimens, with opening ratios of 14% and 22%, respectively, were designed and subjected to axial compression tests. The failure patterns, opening ratios in the core area, and other relevant parameters of the specimens were thoroughly analyzed. Additionally, a finite element model incorporating material non-linearities was developed using ABAQUS (2022) software, and parametric numerical simulations were conducted to further explore the structural response. The results indicated that the variations in the opening ratio had no significant effect on the cracking load of the specimens. However, as the opening ratio increased, the peak load of the compressed columns increased by 8.6%, and the ductility factor increased by 12.9%. The study also reveals that opening ratios below 30%, the casing thickness, and the bolt preload have minimal impact on the bearing capacity of precast columns. These findings provide theoretical support for optimizing hole sizes in dry bolted connections for precast concrete structures. Full article

Following World War II, the swift economic growth in construction and the soaring demand in urban regions led to the excessive extraction of natural resources like fossil fuels, minerals, forests and land. To tackle significant global challenges, including the consumption of natural resources, air pollution and climate change, radical changes have been suggested over the past decades. As part of this strategic initiative, prioritizing sustainability in construction has emerged as a crucial focus in the design of all projects. In order to identify the most environmentally sustainable reinforced concrete (RC) slab system, this research investigates the carbon emissions associated with various slab systems, including solid, voided slabs and precast floor systems. The results demonstrate that beam and slab floor and solid slabs have the highest embodied carbon due to the significant use of concrete and related materials, whereas voided slabs and two-way joist floors exhibit lower carbon emissions. The results indicate that the two-way joist system is the most environmentally advantageous option. For precast floor systems, post-tensioned concrete and hollow-core slabs demonstrate the lowest embodied carbon levels. This research provides practical recommendations for architects and engineers aimed at enhancing sustainable design methodologies. It emphasizes the importance of incorporating low-carbon materials as well as pioneering flooring technologies in upcoming construction initiatives to support the achievement of global sustainability objectives. Full article

Despite the widespread use of precast concrete segmental bridges (PCSBs), concerns persist regarding their structural reliability, particularly due to the interruption of longitudinal reinforcement at joints. To address this, a novel approach based on the Grid Shear Reinforcement Theory is proposed, featuring precast segmental beams with continuous longitudinal reinforcements across joints. Experimental tests were conducted on one monolithic beam and two segmental beams under combined bending and shear with joint types as the primary variable. Key performance metrics included crack propagation, reinforcement strain, failure modes, stiffness, and load-bearing capacity. Results show that continuous longitudinal reinforcement effectively resists axial tension from shear forces, contributing to shear resistance comparable to stirrups. It also restrains diagonal crack propagation and limits main crack widths, significantly improving shear stiffness. Reinforced joints adhered to the plane section assumption and exhibited monolithic beam behavior throughout loading. These findings highlight the critical role of continuous longitudinal reinforcement in segmental beam joints. The study further compares shear reinforcement design approaches in European Codes, ACI, AASHTO, GB, JTC, and the Grid Shear Reinforcement Theory. Practical construction methods for implementing continuous longitudinal reinforcements are also proposed, offering valuable insights for engineering applications. Full article

Based on the tensile strain hardening characteristics of fiber-reinforced cementitious composites (FRCC), this study experimentally investigated the mechanical properties of reinforced concrete (RC) beams reinforced with FRCC, both with and without precast cracks. The spraying process was applied, and different thicknesses of FRCC reinforcement layers were considered. Additionally, crack identification based on Digital Image Correlation (DIC) technology was employed in the study. The results indicated that as the ratio of the thickness of the FRCC reinforcement layer to the beam height increased, the initial cracking load, yield load, and ultimate load of the RC beams after reinforcement also increased. Moreover, the FRCC layer effectively controlled the development of cracks. When considering the damage to existing RC beams, the application of sprayed FRCC reinforcement improved the ultimate flexural capacity of the beams with precast cracks by over 20%. Specifically, a 30 mm FRCC reinforcement layer restored the flexural capacity of damaged RC beams to more than 85% of their uncracked state. Additionally, the use of DIC technology improved the identification of cracks in images and verified the process of damage and cracking in RC beams. Hence, the utilization of sprayed FRCC as formwork-free reinforcement presents significant value in terms of enhancing durability and mechanical properties. Full article

Traditional monolithic precast and precast prestressed concrete joints often face challenges such as complex steel reinforcement details and low construction efficiency. Grouting sleeve connections may also suffer from quality issues. To address these problems, a new precast prestressed concrete frame beam-column exterior joint using ultra-high-performance concrete (UHPC) for connection (PPCFEJ-UHPC) is proposed. This innovative joint lessens the amount of stirrups in the core area, decreases the anchorage length of beam longitudinal reinforcement, and enables efficient lap splicing of column longitudinal reinforcement, thereby enhancing construction convenience. Cyclic loading tests were conducted on three new exterior joint specimens (PE1, PE2, PE3) and one cast-in-place joint specimen (RE1) to evaluate their seismic performance. The study concentrated on failure modes, energy dissipation capacity, displacement ductility, strength and stiffness degradation, shear stress, and deformation’s influence on the longitudinal reinforcement anchoring length and axial compression ratio. The results indicate that the new joint exhibits beam flexural failure with minimal damage to the core area, unlike the cast-in-place joint, which suffers severe core area damage. The novel joint exhibits at least 21.7% and 6.1% improvement in cumulative energy consumption and ductility coefficient, respectively, while matching the cast-in-place joint’s bearing capacity. These characteristics are further improved by 5.5% and 10.7% when the axial compression ratio is increased. The new joints’ seismic performance indices all satisfy the ACI 374.1-05 requirements. Additionally, UHPC significantly improves the anchoring performance of steel bars in the core area, allowing the anchorage length of beam longitudinal bars to be reduced from 16 times of the diameter of reinforcement to 12 times. Full article

To enhance the mechanical properties of precast composite beams, High-Performance Fiber Reinforced Cementitious Composite (HPFRCC) material was used instead of ordinary concrete in the precast shell with reinforced bars to form the R/HPFRCC precast shell composite beam. By controlling different reinforcement ratios, post-longitudinal reinforcement treatment methods, mold shell materials, and loading methods, nine test beams were designed, and four-point bending loading tests were carried out to study the flexural bearing capacity, failure mode, failure process, deformation capacity, and influencing factors of composite beams. The R/HPFRCC prefabricated shell composite beams presented good mechanical performance and integrity. Compared with the RC shell composite beams, the R/HPFRCC prefabricated shell composite beam increased the yield and peak loads by 6.6% and 10.3%, respectively. Using HPFRCC material instead of ordinary concrete in the prefabricated shell could reduce the damage degree of the composite beam under bending. Under the same load, the reinforcement strain in the R/HPFRCC precast shell was smaller than that of the RC precast shell and the cast-in-situ RC beam; thus, the yield of longitudinal reinforcement was effectively delayed. Considering the HPFRCC material mechanical properties, a calculated model for the ultimate load-carrying capacity of R/HPFRCC precast shell composite beams was established. The calculated values were in good agreement with the experimental values. Full article

The longevity and safety of concrete precast crane beams significantly impact the operational integrity of industrial infrastructure. Assessment of surface cracks development in concrete structural elements during laboratory tests is performed mainly by applying standard tools such as linear-variable-differential transformers and strain gauges. This paper presents a novel assessment methodology combining deep convolutional neural network for image segmentation with digital image correlation method to evaluate the structural health of precast crane beams after more than fifty years of service. The study first outlines the adaptation of the deep learning U-Net architecture for detecting and segmentation of surface cracks in crane beams. Concurrently, DIC technique is employed to measure surface strains and displacements under load. The integration of these technologies enables a non-destructive, accurate, and detailed analysis, facilitating early detection of deterioration that may compromise structural safety. Initial results from field tests validate the effectiveness of our approach, demonstrating its potential as a tool for predictive maintenance of aging industrial infrastructure. Full article

The use of recycled aggregates in the manufacture of concrete is presented as a solution to reduce the consumption of resources and waste in the construction sector and contribute to a lower environmental impact. This work aims to explore the possibility of producing structural beams from recycled concrete using aggregates from precast concrete rejects and to improve their design using advanced characterisation techniques. To this end, the experimental data coming from mechanical test and the use of the digital image correlation approach are combined with a robust reliability-based method. The full-field data provided by the digital image correlation approach allow to determine the probabilistic density functions of the mechanical data. From these data, a predictive analysis of the maximum strength and deflection of flexural beams is carried out based on robust design techniques. This approach uses analytical theoretical models and a Monte Carlo-based simulation strategy that allows the prediction of the behaviour of the beams. This methodology was validated by manufacturing six beams with the previously analysed recycled concrete, HA-30, and testing them in the laboratory. All the beams showed behaviour within the predicted range: around 49.7 kN maximum load and just over 9.3 mm maximum deflection. These results demonstrate the robustness of the approach as well as the feasibility of using precast rejects for the manufacture of structural elements. Full article