Search Results (10)

Investigating the seismic damage mechanism of large underground complexes is essential for the safe development of urban underground space. This paper examines a five-story and three-span underground complex situated in a soft soil site. Shaking table tests were designed and conducted on both the free field and the soil–underground complex interaction system. The time–frequency evolution of the free field under various seismic motions was investigated. A combined experimental and numerical simulation approach was employed to examine the seismic response of the soil–underground complex interaction system. The structural deformation evolution, stress distribution, and development process of plastic damage under different seismic motions were analyzed. The results reveal that soft soil exhibits a significant energy amplification effect under far-field long-period ground motions. Structural deformation is mainly governed by horizontal shear. Under strong seismic excitation, plastic damage first initiates at the end of the bottom-story columns and extends to column-to-slab and wall-to-slab connections, where abrupt stiffness changes occur. Under the far-field long-period ground motion, the structural deformation, stress distribution, and plastic damage are significantly greater than those under the Shanghai artificial wave. These findings provide valuable insights for the seismic design of large underground complexes in soft soil sites. Full article

A mid-story pin system to avoid moment-resisting frame column failure during seismic action was proposed recently. The solution consists of a reinforced concrete (RC) pier protruding from the foundations, the steel column connected with the superstructure, and plates and the anchor bolt working as a pinned connection in between. This paper utilizes shell finite element analysis (FEA) models to examine the demanded column-to-beam strength ratio to keep the column elastic and maximize the story drift at the moment of beam buckling of the frame. The method of calculating post-seismic residual strength based on maximal buckling deformation of the beam is also proposed. Full article

Many reinforced-concrete structures collapsed or were seriously damaged in the 7.7 and 7.6 magnitude earthquakes that occurred in southern Türkiye on 6 February 2023. The recorded peak ground accelerations were quite high (2.2 g) and the recorded motions’ elastic acceleration response spectra were significantly greater than the elastic design spectra given by the most recent Turkish seismic design code. A total of 518,000 houses were heavily damaged or collapsed in the eleven cities affected by the earthquake. More than 53,000 people lost their lives and over 100,000 people were injured, the majority of these injurits caused by the collapse of reinforced concrete structures. Post-earthquake damage assessments are important in the context of applying sustainability principles to building design and construction. In this study, post-earthquake damage assesments and evaluations were made for the reinforced-concrete structures that were exposed to destruction or various structural damage in Hatay, Kahramanmaraş and Adıyaman, which where most affected after the Kahramanmaraş earthquakes. The RC building damage and failure mechanisms resulting from field observations were evaluated in detail from a broad performance-based structural and earthquake engineering perspective. Information about Kahramanmaraş earthquakes is given briefly. Design spectra and spectral accelerations were compared for the earthquake stations in these three provinces. Soft/weak story, short column, insufficiently reinforced-concrete, and poor workmanship are the primary causes of structural damage, which cause earthquake weaknesses in these buildings. Full article

Both the biomimetic design based on marine life and the origami-based design are recommended as valuable paths for solving conceptual and design problems. The insights into the combination of the two manners inspired this research: an origami polyhedra-inspired soft robotic jellyfish. The core idea of the story is to leverage the deformation mechanism of the origami metamaterial to approximate the jet-propelled swimming behavior of the prolate medusae. First, four possible variants of origami polyhedra were compared by the hydrodynamic simulation method to determine a suitable model for the soft body of robotic jellyfish. Second, the mathematical model for the jet propulsion performance of the soft origami body was built, and the diameter of the jet nozzle was determined through the simulation method. Third, the overall configuration and the rope-motor-driven driving method of the soft robotic jellyfish were presented, and the prototype was developed. The experimental work of jet swimming, thrust forces measurement, and cost of transport further demonstrated the presented soft robotic jellyfish. In addition, the prospective directions were also discussed to improve maneuverability, sensory perception, and morphological improvement. Due to the advantages, including but not limited to, the concise structure, low cost, and ease of manufacture, we anticipate the soft robotic jellyfish can serve for the ecological aquatic phenomena monitoring and data collection in the future. Full article

Multi-story, old reinforced concrete (RC) structures with a “soft-story” on the ground floor, sustain considerable damage to the soft story during earthquakes due to the presence of masonry infills in the upper stories. Aspects of such masonry infill–RC frame interaction are briefly discussed and a particular retrofitting scheme for the soft story is studied. It consists of RC infills, added within the bays of the ground floor frames and combined with RC jacketing of the surrounding frame, aiming to avert such soft-story deficiency. The impact of such a retrofit is studied through the measured response of 1/3 scaled single-story, one-bay frames subjected to cyclic seismic-type horizontal loads. It is shown that this retrofit results in a considerable beneficial increase in stiffness, strength, and plastic energy consumption. The importance of the presence of effective steel ties connecting this RC infill with the surrounding frame is also demonstrated. In order to achieve these desired beneficial effects to such vulnerable buildings, additional design objectives are established with the aim of avoiding premature failure of the RC infill panel and/or fracture of the steel ties and to protect the surrounding RC frame from undesired local damage. A numerical methodology, which is validated by using the obtained experimental results, is shown to be capable of predicting reasonably well these important response mechanisms and can therefore be utilized for design purposes. Full article

Due to their excellent seismic behavior, shear wall-type concrete buildings are very popular in earthquake-prone countries like Chile. According to current seismic regulations, the performance of such structures can be indifferently assessed through linear or non-linear methods of analysis. Although all the code-compliant approaches supposedly lead to a safe design, linear approaches may be in fact less precise for catching the actual seismic performance of ductile and dissipative structures, which can even result in unconservative design where comparatively stiff buildings like reinforced-concrete shear-wall (RC-SW) buildings are concerned. By referring to a mid-rise multistory RC-SW building built in Chile and designed according to the current seismic Chilean code, the paper investigates the effectiveness of the linear dynamic analyses to predict the seismic performance of such kind of structures. The findings show that the code-compliant linear approaches (Modal Response Spectrum Analysis and Linear Time-History Analysis) may significantly underestimate the displacement demand in RC-SW buildings. This is highlighted by the comparison with the results obtained from the Non-Linear Time-History Analysis, which is expected to give more realistic results. A set of ten spectrum-consistent Chilean earthquakes was considered to carry out the time-history analyses while a distributed-plasticity fiber-based approach was adopted to model the non-linear behavior of the considered building. The paper highlights how the risk of an unsafe design may become higher when reference is made to the Chilean code, the latter considering only the Modal Response Spectrum Analysis (MRSA) without even providing corrective factors to estimate the inelastic displacement demand. The paper checks the effectiveness of some amplifying factors taken from the literature with reference to the case-study shear-wall building, concluding that they are not effective enough. The paper also warns against the danger of local soft-story collapse mechanisms, which are typical of reinforced concrete frames but may also affect RC-SW buildings when weaker structural parts made by column-like walls are present at the ground floor. Full article

The seismic safety of existing building stock has become a very critical issue in recent years, mainly in earthquake-prone South Europe where most of the buildings were designed before the enforcement of seismic standards. Therefore, the concept, development and testing of efficient and cost-effective seismic retrofitting technologies are nowadays strongly needed, both for the society and for the scientific community. This study deals with the seismic assessment of a new RC-framed skin for retrofit intervention of existing buildings, evaluated through nonlinear static (pushover) analyses. A preliminary description of the proposed technology is provided, then numerical modeling of a typical RC existing building before and after retrofitting intervention is performed within the OpenSees framework. The results revealed that the proposed retrofitting technology improves the seismic performance of the RC building, also modifying the failure mode from a brittle soft-story mechanism to a more ductile one. The presented study, dedicated to the structural aspects of the system, is part of the TIMESAFE research project, where the thermo-hygrometric and acoustic performances achievable by the proposed RC-framed skin are also investigated. Full article

To study the influence of masonry infill walls on the hysteretic performance of reinforced concrete frames, a cyclic experiment was conducted for three two-story and two-span reinforced concrete frame structures, including one reinforced concrete frame without infill walls and two frames with infill walls. Whether the infill walls were constructed in the frames and the type of infilled material were the main parameters of the test. The major results reveal that: the infill walls clearly changed the mechanical mechanism of the frame structure at the early stage of loading, magnified the stiffness and horizontal bearing capacity of the frame structure, and enhanced the energy dissipation capacity of the frame structure, but reduced the deformation performance of the frame structure. In the later stage of loading, the infill walls would no longer work as one with the frame gradually with the failure of the infill walls, and the above performance of the structure would approach the empty frame structure. Moreover, the initial stiffness, energy dissipation capacity, and horizontal bearing capacity of the frame with infill walls of clay hollow bricks were the highest among the three specimens. But due to the strong diagonal bracing effect, the damage to the top of the columns and beam-column joints was serious, the yield displacement was reduced significantly, and the shear failure of the top of the columns and the joints occurred prematurely, which showed poor performance of deformation and ductility. However, the frame with infill walls of relatively soft aerated lightweight concrete blocks showed better performance of deformation and ductility. Full article

Base (seismic) isolation is a promising technology for seismic protection of buildings and other constructions. Nowadays, it is accepted that such a technique is efficient and reliable; however, it has two major limitations: soft foundation soil, and tall buildings. The first issue restrains the seismic isolation spreading, given that soft soil is frequent in densely populated areas, and usually such a soil type concentrates the highest seismicity levels. This paper aims to contribute to demonstrating that base isolation, if properly implemented, can be suitable for soft soil. A representative case study is analyzed: a 6-story reinforced concrete (RC) building with base isolation that has recently been built in Shanghai. Since the building is founded on soft soil, concern regarding base isolation suitability arose; even the Chinese design code does not recommend this solution for soft soil. To clarify this issue, non-linear time-history analyses are carried out for a number of natural and artificial seismic inputs that represent the site seismicity; the superstructure behavior is linear, while nonlinearities are concentrated in the isolation layer. The adequacy of base isolation is assessed in the superstructure (in terms of reduction of interstory drift, absolute acceleration and shear force) and in the isolation layer (in terms of axial force, torsion angle and shear strain). The relevance of soil–structure interaction is discussed. The behavior when the mechanical parameters of the isolation units have experienced important changes is also analyzed. The major conclusion is that base isolation of ordinary mid-height RC buildings founded on soft soil can perform satisfactorily in medium seismicity regions. Full article

Reinforced concrete buildings suffered significant damage in the region affected by the 29 May 2011 earthquake in Simav (Kutahya), Turkey. Typical building damage is classified and potential causes of damage are investigated. Reinforced concrete moment resisting frames with hollow brick infill walls are the most common structural system in and around the Simav city center while masonry construction is common in rural areas. Although the Simav earthquake, with a magnitude of 5.7 to 5.9, can be classified as a moderate earthquake, many buildings experienced damage varying from frequent diagonal cracking and brittle failure of infill walls to collapse or severe damage to frames due to short columns, soft stories or other reasons including insufficient or poor detailing of reinforcement. This study investigates and presents the seismicity of the region, characteristics of the measured ground motions, seismic load demands including response spectra, and damage mechanisms, potential causes and classification of observed damage in reinforced concrete buildings. Full article