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Influence of the ultimate strength of stee This study presents a new fiber reinforced polymer tube/filling strengthening method (i.e., FRP tube/filling strengthening) that creates a new composite compression member with a novel mechanical behavior, “bilinear behavior.” Previous experimental and theoretical studies have been conducted based on the ultimate state of the section. To thoroughly study the stiffness and entire loading process of this novel member, finite element analysis (FEA) models are built in this paper. First, the model development process considers the initial defections and interface properties, and these models are verified by the experimental results. Two models of typical load-axial displacement curves describe the experimental results: a Bilinear model and a Trilinear model. Second, finite element modeling (FEM) is used to conduct a parametrical analysis that considers 7 parameters, and the results identify the mechanism of the strengthened member. Specifically, the Bilinear model corresponds to an unreinforced or relatively weakly reinforced specimen, and the Trilinear model corresponds to a relatively strongly reinforced specimen. If the exterior restraint system is weak, then the core steel buckles and subsequently yields; this behavior is described by the Bilinear model. If the exterior restraint system is strong (e.g., the length or the bending stiffness of the exterior restraint system is great), then the specimen can continue to bear a higher force after steel yielding until elastic-plastic buckling occurs; this behavior is described by the Trilinear model. Third, the FEA results and previous experimental and theoretical studies are used to obtain the stiffness and load-axial displacement curves, which are helpful for the design process. In general, relatively accurate FEA models are built in this paper that are capable of describing the mechanical behaviors of the novel member.

Recently, seismic resilience has become a research frontier in civil engineering. The self-centering steel frame can effectively control structural damage and reduce structural residual deformation, which ensures rapid repair after an earthquake. Therefore, such a structural system has attracted extensive attention from researchers. One of the important research directions on self-centering steel frames is the development of high-performance energy-dissipating components. A new type of dual-functional replaceable stiffening angle steel (SAS) component is proposed here. It can effectively improve the stiffness and strength of beam-column connections and has sufficient energy-dissipating performance and ductility. Seven different energy-dissipating components were tested, including one angle steel component and six SAS components. The strength and deformation capacity of the components were compared based on monotonic loading tests. The SAS component with the highest out-of-plane stability and sufficient strength and initial stiffness was selected and subsequently tested under hysteretic loading to investigate its energy-dissipating performance. The theoretical analysis methods of the initial stiffness and the yield moment provided by the SAS components were proposed and validated by the finite-element (FE) models calibrated using experimental data.

Novel hybrid members, namely, CFRP-Al hybrid tubes, which are composed of Al (aluminum alloy) and CFRP (carbon-fiber-reinforced polymer) jackets, represent promising axial load members in civil engineering. Long CFRP-Al hybrid tubes with circular and square hollow sections are investigated in this study using bending and axial compressive buckling tests. Compression buckling analysis is performed using finite element analysis (FEA) and section analysis, which allow one to better understand the unique “partial elastic buckling” behavior of long hybrid members. In addition, a good agreement between FEA and bucking test results is achieved. Finally, based on FEA and the traditional Perry-Robertson formula, the column curves for long CFRP-Al hybrid tubes are given for design.

Regional seismic damage prediction based on multiple-degree-of-freedom shear model and nonlinear time-history analysis can comprehensively consider the characteristics of buildings and ground motions. Two major challenges of applying such methodology, namely (1) parameter determination and (2) damage assessment of buildings in urban scale, are addressed in this study. The reliability of the proposed methods are validated using the tests of three individual buildings and the observed seismic damages of Longtoushan Town in 2014 Ludian earthquake of China. Finally, a regional seismic damage prediction is performed for a large urban region, which demonstrates the applicability and scalability of the proposed methods.

Combining Al (namely, aluminum alloy) and CFRP (carbon-fiber-reinforced polymer) jackets to form structural members can yield many advantages and a bilinear behavior, which can enhance their advantages and mitigate any disadvantages. CFRP–Al hybrid tubes, which are used as axial load members in spatial structures, are investigated in this study by using compression experiments and a theoretical analysis. Formulas that describe the compressive bearing capacity with and without local buckling before yielding are proposed for stub hybrid tubes. In addition, their compressive behaviors are simulated by using the finite element method (FEM). A good agreement in the test results is achieved. The effect of the number of pairs of CFRP layers, the diameter-thickness ratio (DT ratio) and width-thickness ratio (WT ratio), and the fiber direction are described based on finite element analysis (FEA). Finally, a design approach for compressive CFRP–Al hybrid stub tubes is proposed.

Lateral collapses due to earthquakes and progressive collapses due to the sudden destruction of columns are two of the most commonly encountered failure mechanisms for buildings. In a previous study, a novel kinked rebar (KB) configuration was proposed by the authors to simultaneously improve the seismic performance and the progressive collapse resistance of reinforced concrete (RC) frame structures. This configuration works because KB has a weaker initial yielding capacity and larger tensile deformability, and almost the same ultimate tensile capacity compared to ordinary steel rebar. This paper aims to provide further experimental validation and enhance the understanding of the seismic performance of RC beams with KB configurations. First, to overcome the disadvantages of the application of KB found in a previous study, the middle longitudinal bars in an RC beam were proposed to further improve the KB configuration. Second, cyclic loading tests of bare KB specimens were conducted to investigate the hysteresis equivalent stress-equivalent strain curves and failure modes of KB. Third, a cyclic loading test of RC beams with KB was performed. The test results showed that the application of KB could help relocate the plastic hinges to protect the RC column and joint, weaken the yielding loading capacity of the beams to increase the strong column-weak beam (SCWB) ratio, and increase the loading capacity of the beam again at large rotations to maintain a certain lateral load resistance at large deformation of the frame structure. An interesting “two-hinge” behavior was also found in the tests for RC beams with the KB configuration.

A novel column consisting of steel, concrete and fiber-reinforced polymer (FRP) is presented and assessed through experimental study. The sectional form of steel–concrete–FRP–concrete (SCFC) columns has a square steel tube as the outer layer and a circular filament-wound FRP tube as the inner layer, and concrete is filled between these two layers and within the FRP tube. Thus the column can be regarded as a concrete-filled square steel tube (CFST) with a FRP-confined concrete core (FCCC). In comparison to existing composite column sections, several advantages are achieved such as ease of connection to beams, the stronger confinement of core concrete, ductile response, and residual load capacity. 18 SCFC stub columns are tested with different concrete strengths, FRP tube thickness and steel tube thickness in comparison to four traditional composite columns. The distinctive behaviors of SCFC columns, including significant post-yield stiffness, ductile failure, and stable residual bearing capacity are found. Test results show that the strengths of concrete, FRP, and steel are effectively utilized at different stages, including the initial linear stage, the secondary linear stage (hardening stage), and the post-peak stage. The influences of key design parameters on the mechanical characteristics of initial compressive stiffness, peak strain, residual load-bearing capacity, and ductility are also clarified.

Summary To evaluate the major differences between the Chinese and the United States (US) seismic design codes from a structural system viewpoint, a comparative case study is conducted on a tall frame-core-tube building, a typical type of reinforced concrete system widely constructed in both countries. The building, originally designed using the US seismic design code, is firstly redesigned according to the Chinese seismic design code based on the information provided by the Pacific Earthquake Engineering Research Center. Secondly, the member dimensions, the dynamic characteristics, the seismic design forces and the material consumptions of the two designs are compared in some detail. Subsequently, nonlinear finite element models of both designs are established to evaluate their seismic performances under different earthquake intensities. Results indicate that the seismic design forces determined by the Chinese response spectrum are larger than those determined by the US spectrum at the same seismic hazard level. In addition, the upper-bound restriction for the inter-story drift ratio is more rigorously specified by the Chinese code. These two aspects have led to a higher level of material consumption for a structure designed by the Chinese code. Despite of the above discussions, the two designs yield roughly similar structural performances under earthquakes. Copyright © 2015 John Wiley & Sons, Ltd.

Numerous field tests indicate that the soil–structure interaction (SSI) has a significant impact on the dynamic characteristics of super-tall buildings, which may lead to unexpected structural seismic responses and/or failure. Taking the Shanghai Tower with a total height of 632 m as the research object, the substructure approach is used to simulate the SSI effect on the seismic responses of Shanghai Tower. The refined finite element (FE) model of the superstructure of Shanghai Tower and the simplified analytical model of the foundation and adjacent soil are established. Subsequently, the collapse process of Shanghai Tower taking into account the SSI is predicted, as well as its final collapse mechanism. The influences of the SSI on the collapse resistance capacity and failure sequences are discussed. The results indicate that, when considering the SSI, the fundamental period of Shanghai Tower has been extended significantly, and the collapse margin ratio has been improved, with a corresponding decrease of the seismic demand. In addition, the SSI has some impact on the failure sequences of Shanghai Tower subjected to extreme earthquakes, but a negligible impact on the final failure modes.

During a bridge service life, many factors can cause damage accumulation such as overloaded traffic, fatigue effect, and so on. Hence, the identification of potential damages has been received wide attention to prevent such sudden fatal accident. An experiment of a continuous rigid frame concrete bridge, which had 3 spans and a total length of 18 meters, was presented in this paper. Two load stages and ten different load steps were simulated to test various scenario of long-term loading and different levels of overload. Curvature mode method was adopted to detect the damage during the exercises. The changes of curvature modes were used to detect damage after the ten load steps. This method performed excellent to identify the damage position of the bridge. So, it is concluded that the curvature modes can be used to detect damage in actual structures. In addition, the Finite-Element Analysis (FEA) was utilized, and the experimental recurring was verified positively through FEA model.

Single-Degree-of-Freedom (SDOF) systems are widely used to investigate the collapse resistance of building structures. A SDOF model capable of representing the key properties associated with earthquake-induced collapse is outlined in this study. The seismic collapse capacity of SDOF systems is evaluated via an incremental dynamic analysis, based on which the collapse capacity spectrum is developed. The computational procedure and engineering significance of the collapse capacity spectrum are elaborated in some detail. The influence of various structural properties on the collapse resistance of SDOF structural systems is also comprehensively discussed, which include fundamental period, ductility ratio, post-capping stiffness, hysteretic pinching, cyclic deterioration and P-Δ effect. Furthermore, the influence of ground motion features on the collapse resistance of SDOF systems is examined by using the proposed collapse capacity spectrum.

Progressive collapse is a mechanical process that exhibits nonlinear and dynamic characteristics. The nonlinear dynamic effect on the progressive collapse resistance demand can be accurately evaluated by the nonlinear dynamic (ND) method. In engineering practice, however, the simplified and easy-to-use linear static (LS) method is often adopted. That is accomplished by using a dynamic amplification factor (DAF) to correct the LS resistance demand to approximate the true ND resistance demand. In this paper, the analytical expression of the DAF is established based on the energy conservation principle. The collapse-resisting substructure is firstly simplified as a single-degree-of-freedom (SDOF) equivalent. Then the energy conservation equation and the static balance equation of the SDOF equivalent are established to obtain the ND and LS demands. Finally, the DAF is obtained by dividing the ND demand by the LS demand. The DAF is validated through a series of the numerical examples including a SDOF system, a 3-storey planar frame and an 8-storey 3-D RC frame model structures.

The seismic design of super-tall buildings has become an important research topic in earthquake engineering. Limited research has been conducted on the distribution of plastic energy dissipation among the different components of super-tall buildings when subjected to strong earthquakes. A simplified two-dimensional (2D) nonlinear model is developed based on the analysis of Shanghai Tower, an actual super-tall building with a total height of 632 m. The accuracy of the simplified model is validated by comparing the results from modal analyses, and static and dynamic time-history analyses of the refined finite element model. Then, the proposed simplified model is used to determine the plastic energy dissipation of different components and the distribution of the total plastic energy dissipation over the height of the Shanghai Tower under different seismic intensities. The analysis indicates that the total plastic energy is mainly concentrated in the upper four Zones of the building and that the outrigger is the major plastic energy dissipation component in the Shanghai Tower.

A double-column self-centering pier fused with shear links is a novel structure developed to reduce residual deformation and facilitate post-earthquake repair. With this novel structure, the seismic resilience of bridges can be improved, and the reliability of lifeline infrastructure can be ensured. This paper presents the proposed pier configuration and investigates the mechanical behavior of the pier. A simplified finite element model is established to develop the lateral force-displacement relationship under cyclic loading. Additionally, a theoretical model based on the matrix displacement method and the virtual work principle is proposed to calculate the lateral force-displacement skeleton curve. The rationality and reliability of the theoretical model are validated by the satisfactory agreement observed between the numerical and theoretical results. Furthermore, a series of parametric analyses are conducted to discuss the effects of key parameters. The outcomes of this work can serve as a reference for further development of the design method for the innovated pier.

A novel ring-beam connection is proposed for steel reinforced concrete (SRC) columns and reinforced concrete (RC) beams, avoiding difficult design and complex construction. The seismic performance of this ring-beam connection is investigated through experimental tests and finite element analysis (FEA). Four reduced-scale specimens were tested under cyclic loading to examine the effects of longitudinal reinforcements, stirrups and different anti-shear parts in the ring-beam connection. The results from tests show that the ring-beam connections with an appropriate design have a good seismic performance and satisfy strong connection weak beam requirement effectively. As further investigation, finite element analyses are carried out, and the analyses results agree well with the experiments.

Ground motion intensity measures ( IMs) are an important basis of structural seismic design. Extensive research has been conducted on the selection of IMs for building structures with fundamental periods shorter than 6 s. However, minimal work has been performed for super high-rise buildings whose fundamental periods are much longer than 6 s. To fill the gap in this research area, this paper aims to develop a simplified analytical model for super high-rise buildings based on the flexural-shear coupled beam model. The variation in correlation and dispersion between different IMs is evaluated and the structural seismic response demand measures ( DMs) are analyzed for different structural fundamental periods. Subsequently, rational IMs for the seismic design of super high-rise buildings are suggested. In addition, the influence of different flexural and shear stiffness ratios, α0, on the selection of an IM for super high-rise buildings is also discussed. Finally, a series of incremental dynamic analyses (IDA) of the Shanghai Tower, with a total height of approximately 632 m, is performed to verify the rationality of using different IMs for super high-rise buildings. The numerical results indicate that with a minimum dispersion, the peak ground velocity (PGV) has a better correlation to the story drift ratio than any other IMs. While considering structural nonlinearity, PGV still yields the minimum coefficient of variation in the collapse analysis of the actual super high-rise building. It is therefore recommended that PGV be used as an IM for the seismic design of super high-rise buildings.

This paper reports on axial compression experiments on 18 specimens that were strengthened using fiber-reinforced polymer (FRP) fabric and bamboo sticks to improve buckling resistance. The core steel members were first bundled with bamboo sticks longitudinally using steel wire and were then wrapped longitudinally and laterally with FRP fabric. The bending stiffness and load-bearing capacity of the members were increased by the strengthening system, and the bamboo sticks acted as lightweight and free-shaped filling between the steel and FRP. Three major parameters were examined: (1) the cross-sectional shape; (2) the nominal slenderness ratio of the steel members; (3) the number of FRP fabric layers. Although global buckling that is analogous to that in unstrengthened specimens was observed, the strengthened specimens exhibited significant local deformation at the end of the steel member and rupture of the FRP fabric at midheight. The load-displacement results demonstrated an increase of 25–114% fo...

Ground motion intensity measure (IM) is an important part in performance-based seismic design. A reasonable and efficient IM can make the prediction of the structural seismic responses more accurate. Therefore, a more reasonable IM for super high-rise buildings is proposed in this paper. This IM takes into account the significant characteristic that higher-order vibration modes play important roles in the seismic response of super high-rise buildings, as well as the advantages of some existing IMs. The key parameter of the proposed IM is calibrated using a series of time-history analyses. The collapse simulations of two super high-rise buildings are used to discuss the suitability of the proposed IM and some other existing IMs. The results indicate that the proposed IM yields a smaller coefficient of variation for the critical collapse status than other existing IMs and performs well in reflecting the contribution of higher-order vibration modes to the structural response. Hence, the proposed IM is more applicable to seismic design for super high-rise buildings than other IMs.

A strengthening approach to improve the buckling resistance of steel members in compression is introduced in this paper, where a mortar-filled FRP tube is sleeved outside the steel member and wrapped with FRP fabrics at the ends of the tube. Through axial compression tests on 18 specimens with bi-axial symmetrical cross-section, the load–strain development and failure modes were obtained and improved load bearing capacity and ductility were evidenced. The effects of the cross-section of core steel, slenderness and FRP fabric layers wrapped at the ends of specimens were investigated. It was found that, after strengthening, the failure modes changed from steel yielding at the mid-height of the steel member due to global buckling to local damage at the steel end. As a result, the load bearing capacity increased by 44–215% and ductility increased by up to 877%. The segmentation model was developed for strengthened specimens, by which the calculated load bearing capacity agrees well with the experimental result.

Research on earthquake-induced collapse simulation has a great practical significance for super-tall buildings. Although mega-braced frame-core tube buildings are one of the common high-rise structural systems in high seismic intensity regions, the failure mode and collapse mechanism of such a building under earthquake events are rarely studied. This paper thus aims to investigate the collapse behavior of a super-tall mega-braced frame-core tube building (H = 550 m) to be built in China in the high risk seismic zone with the maximum spectral acceleration of 0.9 g (g represents the gravity acceleration). A finite element (FE) model of this building is constructed based on the fiber-beam and multi-layer shell models. The dynamic characteristics of the building are analyzed and the earthquake-induced collapse simulation is performed. Finally, the failure mode and mechanism of earthquake-induced collapse are discussed in some detail. This study will serve as a reference for the collapse-resistance design of super-tall buildings of similar type.

In recent years, the rapid development of super tall buildings has become a frontier in civil engineering. Subjected to service level earthquakes, all of the plastic energy dissipation components are still in the elastic stage, and will not dissipate energy. In this situation, the story acceleration will be magnified several times, resulting in the comfort problem and causing the damage of contents in the building and other non-structural components. It will not only bring serious economic losses, but also affect the normal function of the building. Therefore, corresponding measures should be proposed to reduce the story acceleration of super tall buildings under service level earthquakes. A simplified analytical model for super tall buildings based on the flexural-shear coupling beam model is developed in this work. Based on the simplified model with a super TMD on the top of the building, the control effect of TMD on the story acceleration is studied by time history analysis. The optimal frequency of TMD is determined through parametric discussion. The outcome of this study can provide some references for the engineering design and vibration reduction of super tall buildings.

SUMMARY Collapse resistance of high-rise buildings has become a research focus because of the frequent occurrence of strong earthquakes and terrorist attacks in recent years. Research development has demonstrated that numerical simulation is becoming one of the most powerful tools for collapse analysis in addition to the conventional laboratory model tests and post-earthquake investigations. In this paper, a finite element method based numerical model encompassing fiber-beam element model, multilayer shell model, and elemental deactivation technique is proposed to predict the collapse process of high-rise buildings subjected to extreme earthquake. The potential collapse processes are simulated for a simple 10-story RC frame and two existing RC high-rise buildings of 18-story and 20-story frame–core tube systems. The influences of different failure criteria used are discussed in some detail. The analysis results indicate that the proposed numerical model is capable of simulating the collapse process of existing high-rise buildings by identifying potentially weak components of the structure that may induce collapse. The study outcome will be beneficial to aid further development of optimal design philosophy. Copyright © 2012 John Wiley & Sons, Ltd.

The concepts of seismic isolation and energy dissipation structures emerged in the early 1970s. In China, the first seismic isolation structure was finished in 1993, and the first energy dissipation structure was built at about the same time. Up to 2007, China had more than 600 seismic isolation and about 100 energy dissipation building structures. In 2008, the huge Wenchuan earthquake hit the southwest of China, which triggered a bloom of new seismic isolation and energy dissipation structures. This paper presents the development history and representative applications of seismic isolation and energy dissipation structures in China, reviews the state-of-the-practice of Chinese design, and discusses the challenges in the future applications. Major findings are as follows: Basic design procedures are becoming standardized after more than ten years of experiences, which mainly involve determination of design earthquake forces, selection of ground motions, modeling and time-history analyses, and performance criteria. Nonlinear time-history analyses using multiple ground motions are the characteristic of the design of seismic isolation and energy dissipation structures. Regulations, standardization and quality control of devices, balance between performance and cost, comparison with real responses, and regular inspection are identified as the issues that should be improved to further promote the application of seismic isolation and energy dissipation structures in China.

Seismic design should quantitatively evaluate and control the risk of earthquake-induced collapse that a building structure may experience during its design service life. This requires taking into consideration both the collapse resistant capacity of the building and the earthquake ground motion demand. The fundamental concept of uniform-risk-targeted seismic design and its relevant assessment process are presented in this paper. The risks of earthquake-induced collapse for buildings located in three seismic regions with the same prescribed seismic fortification intensity but different actual seismic hazards are analyzed to illustrate the engineering significance of uniform-risk-targeted seismic design. The results show that with China’s current seismic design method, the risk of earthquake-induced collapse of buildings varies greatly from site to site. Additional research is needed to further develop and implement the uniform-risk-targeted seismic design approach proposed in this paper.

In order to study the dynamic performance of seismically isolated bridges under the most unfavorable loads in the longitudinal direction, a dynamic equation for vehicle braking in the longitudinal direction is established. A four or fiveorder Runge-Kutta method is adopted to obtain the time-history response of a wheel set under braking force. The quadratic discretization method is then used to transform this time-history into a braking and bending force time-history of a structural fixed node, and a dynamic response analysis of the seismically isolated bridge under the vehicle’s braking force is carried out using ANSYS, a universal finite element analysis software. According to the results, seismic isolation design results in a more rational distribution of braking force among piers; the influence of the initial braking velocity on the vehicle braking force is negligible; the location where the first wheel set leaves the bridge is the most unfavorable parking location; a seismic isolation bridge bearing constructed according to typical design methods enters into a yield stage under the braking force, while the shearing force at the bottom of the pier declines as the isolation period is extended; the design requirements can be met when the yield displacement of the seismic isolation bearing is less than 5 mm and the yield strength is greater than the braking force.

Fiber-reinforced polymer (FRP) strengthening technique to improve buckling resistance of steel members is presented in concept and experimental demonstration. The conceptual design of this method is introduced through the preliminary experiments on three specimens. Then, another 14 specimens are tested under axially compressive loading, by which the compressive behavior and the strengthening effects are investigated considering different design parameters and configuration, including the slenderness ratio, the confinement detail, the filled materials and the end connection. The strengthening effects are analyzed by the comparison of both theoretical and test results, which show that the overall buckling failure of steel members can be prevented by FRP strengthening and the ultimate loading capacity and deformation capacity of steel members are enhanced considerably. The maximum load-bearing capacity of strengthened members is 2.86 times of the nonstrengthened ones, and the failure maintains a ductile behavior. In addition, the load-bearing capacity of the members strengthened in this way is compared with the Euler loads of the original steel member and the composite member.

Buckling-restraint braces (BRBs) are used extensively in seismic-resistant structures. They consist of a core energy dissipation and external restraining component. A novel glass fiber–reinforced polymer (GFRP) steel BRB is proposed. In the GFRP steel BRB, four GFRP pultruded tubes, which are tied together by GFRP wrapping layers, are used to restrict core steel component buckling instead of conventional steel tube and infilled concrete or mortar. This GFRP steel BRB is extremely lightweight. Techniques for manufacturing GFRP steel BRB were developed for convenient large-scale industrialized production. Quasi-static tests were carried out to validate the performance of the GFRP steel BRB under cyclic loading. The tests focused mainly on energy dissipation capacity and ultimate failure mode of the proposed GFRP steel BRB. The effect of applying additional reinforcements to the GFRP external restraining component on the performance of GFRP steel BRB was also investigated. The performance of the appr...

Nonlinear static analysis (or pushover analysis) has been widely used in the last decade as a simplified and approximate method to evaluate the structural seismic performance and to estimate inelastic structural responses under severe ground motions. However most currently used pushover procedures with invariant lateral load patterns cannot fully reflect the effect of higher-order modes on structural dynamic responses. To overcome such a problem, a so-called Modal Pushover Analysis (MPA) was proposed based on the modal decoupling response spectrum method where the effect of higher modes was considered. To date, most research on MPA has been focused on frame structures. In engineering practice, however, most medium-to high-rise building structures are in the form of frame-shear-wall. Therefore it is necessary to extend the current research activity to implement the MPA to frame-shear-wall structures. In this study, two reinforced concrete frame-shear-wall structures of 10 and 18 stories are analyzed to evaluate the performance of the MPA method and the pushover procedures with invariant load patterns. The evaluation is based on the “exact” solutions of a nonlinear dynamic time-history analysis. The results show that the MPA method including higher-order modes is more accurate than the other pushover procedures. This is more evident when estimating structural responses for high-rise structures than the medium-rise counterparts.

Progressive collapse of structures refers to local damage due to occasional and abnormal loads, which in turn leads to the development of a chain reaction mechanism and progressive and catastrophic failure. The tie force (TF) method is one of the major design techniques for resisting progressive collapse, whereby a statically indeterminate structure is designed through a locally simplified determinate structure by assumed failure mode. The method is also adopted by the BS8110-1:1997, Eurocode 1, and DoD 2005. Due to the overly simplified analytical model used in the current practical codes, it is necessary to further investigate the reliability of the code predictions. In this research, a numerical study on two reinforced concrete (RC) frame structures demonstrates that the current TF method is inadequate in increasing the progressive collapse resistance. In view of this, the fundamental principles inherent in the current TF method are examined in some detail. It is found that the current method fails to consider such important factors as load redistribution in three dimensions, dynamic effect, and internal force correction. As such, an improved TF method is proposed in this study. The applicability and reliability of the proposed method is verified through numerical design examples.

According to the Code for Seismic Design of Buildings (GB50011-2001), ten typical reinforced concrete (RC) frame structures, used as school classroom buildings, are designed with different seismic fortifi cation intensities (SFIs) (SFI=6 to 8.5) and different seismic design categories (SDCs) (SDC=B and C). The collapse resistance of the frames with SDC=B and C in terms of collapse fragility curves are quantitatively evaluated and compared via incremental dynamic analysis (IDA). The results show that the collapse resistance of structures should be evaluated based on both the absolute seismic resistance and the corresponding design seismic intensity. For the frames with SFI from 6 to 7.5, because they have relatively low absolute seismic resistance, their collapse resistance is insuffi cient even when their corresponding SDCs are upgraded from B to C. Thus, further measures are needed to enhance these structures, and some suggestions are proposed.

In recent years, super high-rise buildings (>500 m) are developing very quickly and become an important frontier of civil engineering. The collapse resistance of super high-rise buildings subjected to extremely strong earthquake is a critical problem that must be intensively studied. This paper builds up a nonlinear finite element model of the tallest building in China, Shanghai Tower (632 m), and proposes the modeling method and failure criteria for different structural elements. The dynamic characters of this building are then analyzed, and the possible failure modes and collapse processes due to earthquakes are predicted, as well as the corresponding collapse mechanism. This work will be helpful in collapse prevention and the seismic design of super high-rise buildings.

A “mega-earthquake” is one with an intensity larger than the most severe earthquake intensity category currently considered in design codes. For a “mega-earthquake,” the design objective of a given structure is to “preserve living spaces for people in the buildings.” In this paper, factors that may influence the collapse resistance of RC frames in a megaearthquake are analyzed based on seismic damage observed in the 2008 Wenchuan earthquake. Methodologies to improve structural collapse resistance focus on three aspects: global strength margin, global redundancy and global integration of the structural system. Fundamental principles and design concepts for collapse prevention under a mega-earthquake are proposed, and issues that need further research are identified.

By taking building structures as systems, the difference between the safety margins of a structure and that of its element is clarified and the robustness of the structure to resist unexpected disasters is discussed. The system concept is further used to introduce the concepts of importance levels and functionality levels in structural systems, the designability of structural systems is then pointed out. The local and global failure mechanisms of building structures under earthquake are summarized, and the failure mechanism control method is discussed based on the concepts of system and designability. For global failure mechanism, the desirable seismic performance is put forward, and at last some practical methods to control the seismic failure mechanism and the failure procedures are proposed based on the hierarchy concept of the structural system.

Fiber reinforced polymer (FRP) is suitable for structures in corrosive environment and long-span lightweight structures due to its high-strength, light-weight, and anti-corrosive qualities. The behavior of pultruded glass fiber reinforced polymer (GFRP) pipes, which are the members of long-span lattice structures, under axial compression was investigated by tests. Short GFRP pipes were first tested to determine the basic mechanical properties. Then the stability of long GFRP pipes was studied by axially compressive tests in four groups with different slenderness ratios, twelve specimens totally. Based on the results of the tests and literature, the formula of the buckling load of composite pipes under axially compressive load was presented based on Perry formula. It can well predict the buckling failure load GFRP pipe under axial compression.

A novel distributed tuned liquid damper (DTLD) for reducing vibration in structures is proposed in this paper. The basic working principle of the DTLDs is to fill the empty space inside the pipes or boxes of cast-in-situ hollow reinforced concrete (RC) floor slabs with water or other liquid. The pipes or boxes then work as a series of small TLDs inside the structure, to increase the damping ratio of the entire structural system. Numerical simulation that accounts for the fluidstructure coupling effect is carried out to evaluate the vibration-reduction efficiency of the DTLDs. The results show that the DTLDs are able to considerably increase the damping of the structure and thus reduce its vibration. An additional benefit is that the DTLDs do not require architectural space to be added to the structure.

The three dimensional (3D) printing technology has undergone rapid development in the last few years and it is now possible to print engineering structures. This paper presents a study of the mechanical behavior of 3D printed structures using cementitious powder. Microscopic observation reveals that the 3D printed products have a layered orthotropic microstructure, in which each layer consists of parallel strips. Compression and flexural tests were conducted to determine the mechanical properties and failure characteristics of such materials. The test results confirmed that the 3D printed structures are laminated with apparent orthotropy. Based on the experimental results, a stress–strain relationship and a failure criterion based on the maximum stress criterion for orthotropic materials are proposed for the structures of 3D printed material. Finally, a finite element analysis was conducted for a 3D printed shell structure, which shows that the printing direction has a significant influence on the load bearing capacity of the structure.

Severe earthquakes continue to cause major catastrophes. Many devices in active, hybrid, and semi-active structural control systems which are used as controllable force devices are costly to build and maintain. The passive control reinforced concrete frame (PCRCF) reinforced with high strength steel only in the columns presented here provides structural systems more resistance to lateral earthquake loadings at comparatively lower cost. The effectiveness is demonstrated by a nonlinear static analysis using fiber model for a single story single bay frame. The study shows that the use of high performance steel in columns prevents formation of plastic hinges at the critical column base sections and failures are always initiated by reinforcement yielding at the beam ends. Furthermore, after experiencing severe lateral drift, the passive control design has small residual displacements compared to ordinary reinforced concrete frames. PCRCF rehabilitation and strengthening can be achieved more easily as compared with ordinary reinforced concrete frame.

A crack model for the fracture in concrete based on meshless method is proposed in this paper. The cracks in concrete are classified into micro-cracks or macro-cracks respectively according to their widths, and different numerical approaches are adopted for them. The micro-cracks are represented with smeared crack approach whilst the macro-cracks are represented with discrete cracks that are made up with additional nodes and boundaries. The widely used meshless method, Element-free Galerkin method, is adopted instead of finite element method to model the concrete, so that the discrete crack approach is easier to be implemented with the convenience of arranging node distribution in the meshless method. Rotating-Crack-Model is proved to be preferred over Fixed-Crack-Model for the smeared cracks of this composite crack model due to its better performance on mesh bias. Numerical examples show that this composite crack model can take advantage of the positive characteristics in the smeared and discrete approaches, and overcome some of their disadvantages.

An accurate local bond–slip model is of fundamental importance in the modelling of FRP-strengthened RC structures. In this paper, a review of existing bond strength models and bond–slip models is first presented. These models are then assessed using the results of 253 pull tests on simple FRP-to-concrete bonded joints, leading to the conclusion that a more accurate model is required. In the second half of the paper, a set of three new bond–slip models of different levels of sophistication is proposed. A unique feature of the present work is that the new bond–slip models are not based on axial strain measurements on the FRP plate; instead, they are based on the predictions of a meso-scale finite element model, with appropriate adjustment to match their predictions with the experimental results for a few key parameters. Through comparisons with the large test database, all three bond–slip models are shown to provide accurate predictions of both the bond strength (i.e. ultimate load) and the strain distribution in the FRP plate.

External bonding of fiber-reinforced polymer (FRP) plates or sheets has recently emerged as a popular method for the strengthening of reinforced concrete (RC) structures. The behavior of such FRP-strengthened RC structures is often controlled by the behavior of the interface between FRP and concrete, and this interfacial behavior is commonly studied through a pull test in which an FRP sheet or plate is bonded to a concrete prism and is subject to tension. In this paper, a meso-scale finite element (FE) model implemented with the MSC.MARC program is presented for the simulation of interfacial debonding failures in a pull test. In this model, very small nearly square elements (0.25–0.5 mm in size) are used with the fixed angle crack model (FACM) to capture the d evelopment and propagation of cracks in the concrete layer adjacent to th ea dhesive layer. The effect of element size is taken into account in modeling both the tensile and shear behavior of cracked concrete. Comparisons between the predictions of this model and test results ar ep resented to demonstrate the capability and accuracy of this FE model. Th ed ebonding mechanism is also examined using results obtained with the FE model. Finally, a method for the determination of the local bond–slip curve of the FRP-to-concrete interface from the FE results is described. © 2005 Elsevier Ltd. All rights reserved.

Seven specimens were tested to investigate the shear strength of reinforced concrete (RC) columns strengthened by wrapping with a carbon-fiber-reinforced plastic sheet. All specimens were tested under lateral reversal cyclic loading and a constant axial load. The main parameters considered were the carbon-fiber-reinforced plastic (CFRP) sheet amount, the shear span/depth ratio, and the axial load ratio. Many strain gauges were attached to the CFRP sheet to obtain its shear contribution. It was found that the shear behavior of the RC part of the strengthened column was almost the same as that of the unstrengthened one. The parameters were found to have an influence on the shear contribution of the CFRP sheet, which could be explained by truss-arch shear resistance mechanism. A simple superposition method is suggested to calculate the shear strength of the strengthened column, in which a shear coefficient (v) is proposed to evaluate the shear contribution of the CFRP sheet based on the test results. The calculated results of suggested method are shown to be in reasonable agreement with test ones.