Journal of Earthquake and Tsunami

In this paper, a new idea for designing the metallic yielding–friction damper (MYFD) is presented based on the principle that the metallic plate can be used for yielding and can be the friction component of the passive energy dissipation device (PEDD). This type of damper is so-called the MYFD, because it consists of yielding part and friction part. Phased energy dissipation is realized throughout the metallic yielding plate and friction plate combination where friction behavior is prior to yielding behavior. The quasi-static test with two small-scale MYFDs is carried out. Then, it is applied in an actual reinforced concrete building. The design method and fitting process of the MYFDs are introduced. In order to compare seismic responses of the building with and without the dampers, a dynamic analysis of the building under earthquakes is performed. The results show that the MYFD presented here possess good ability of seismic energy dissipation.

The concept of self-centering structure and replaceable structural member or fuse is a new approach of earthquake resilient structural design. The new structural system is not only capable of preventing from failure of the structure and life safety of the occupants during earthquakes, but also quickly restoring its basic function in a short time following earthquakes. Restoring the original position through self-weight or pre-stressing forces, this kind of structures is defined as a rocking or self-centering structure. The replaceable elements of the other new kind of structural system, which includes coupling beams, energy dissipation devices, and rubber bearings and so on, are designed to be inelastic or failure, like a fuse, and to protect the main structure from damage in the region of high seismicity. The authors of this paper will report three different tests on new earthquake resilient structures, which are shaking table tests on a self-centering RC frame, quasi-static cyclic tests on RC wall with replaceable coupling beams and the ones with replaceable foot parts. All of the three new kind structural systems present an efficient resilient ability under severe horizontal forces in the tests.

In the study, a novel microcapsule technology based self-healing system for concrete structures has been developed. Through situ-polymerization reaction, the microcapsule is formed by urea formaldehyde resin to pack the epoxy material, which is applied to cementitious composite to achieve self-healing effect. The experimental results revealed that the self-healing efficiency of the composite can be accessed from the recovery of the permeability and strength for the cracked cementitious specimens as the healing agent in the microcapsule acting on the cracks directly. Scanning electronic microscope (SEM/EDX) results show that the epoxy resin is released along with the cracking of the cementitious composite and prevent from cracks continued growth. Further studies show that the self-healing efficiency is affected by the pre-loading of composite, particle size of microcapsule, aging duration of healing agent and so on.

In this paper, the durability of steel fiber reinforced concrete/SFRC is tested under the combined effects of carbonization and acid rain erosion. Mass loss rate, splitting tensile strength loss rate, eroded thickness and neutralization depth were taken as evaluation index. Test results indicated that the concrete mass loss rate, splitting tensile strength loss rate, and eroded thickness of SFRC under the multi-combined effects of acid rain and carbonization are greater than that of SFRC affected by the acid rain; the neutralization depth of SFRC are larger under the multi-factor effects of acid rain and carbonization compared to the superposition of them. According to the analysis of combined effects, the carbonization and acid rain has almost equal contribution to the neutralization of concrete. Proper mixture of steel fiber can effectively inhibit the erosion of original concrete under the effect of acid rain and reduce the neutralization depth. According to the varied mixing proportions in the test, the SFRC with the steel fiber mixing proportions of 1.5% has the best durability.

A pressure impulse (PI) diagram is a useful preliminary design tool for structural members against blasts. An extensive amount of investigation has been undertaken to generalize PI curves, using single degree of freedom (SDOF) theory, for elastic structural members. In this study, a new original approach also using SDOF theory, relying on the concept of effective pulse shape, is presented for determining a PI curve for any elastic member. The advantage of this approach is that it can be applied to any given type of blast load. The techniques and equations involved in this approach are outlined. Then, to assess the accuracy of this approach, elastic normalized PI curves generated using the new approach are compared against those obtained using the traditional methods. Finally, this approach is compared against other simplified techniques for determining elastic normalized PI curves.

Structural response to high impulsive loads such as impact and blast involves a series of dynamic effects of distinctive characteristics. These vary from the high intensity, high strain rate effect at the material level; various dynamic modes and failure mechanisms at the structural component level; to the dynamic amplification associated with the transition to a typical double-span mechanism in the process of the progressive collapse due to a sudden removal of vertical load carrying member(s). This paper discusses the characteristics of these different dynamic effects and introduces some associated research studies. The governing mechanisms in the different regimes of dynamic effects are highlighted and appropriate analytical and numerical modeling approaches are discussed.

This paper investigates the isolation performances of bid DB02 section of the Hong Kong–Zhuhai–Macao Bridge. The navigable cable-stayed bridge and the non-navigable steel-concrete continuous girder bridge in the high-pier and low-pier regions are taken as an illustration. The finite element models with aseismatic bearings and isolated bearings are established and the seismic time-history analysis under the earthquake levels of P2 and P3 are carried out. The nonlinear properties of LRB, HDR, and FPB isolated bearings and the pile-soil interaction are simulated using bilinear spring elements and layered Winkler soil springs model, respectively. The results show that the bridge structure with isolated bearings is more flexible by extending vibration period. The dissipated hysteric energy can effectively reduce the earthquake energy and the response of the structure. Subject to the earthquake level P3, most piers of the bridge are in elastic state. Subject to the earthquake level P2, the bridge is in perfect elastic state. The isolating effect of the isolated bearings to the continuous girder bridge is better than the cable-stayed bridge with tower and beam consolidation.

Seismic induced pounding damage to bridge structures was repeatedly observed in many previous major earthquakes. To avoid this adverse effect, extensive research efforts have been made by many researchers. This paper presents a state-of-the-art review in this field. It includes a brief review of the numerical modeling of bridge structures and impact models, numerical simulation of pounding responses between different components of bridge structures, experimental investigations, and pounding mitigation methods.

Under strong winds, bridges may exhibit large dynamic responses. Wind may also endanger the safety of moving vehicles on the roadways as well as on bridges. For regular aerodynamic study of long-span bridges, traffic loads are not typically considered, assuming that bridges will be closed to traffic at high wind speeds. Therefore, bridges are usually tested in wind tunnels or analyzed numerically without considering moving vehicles on them. However, there are numerous possible scenarios under which vehicles may still be on the bridge when higher wind speeds occur. These scenarios include unexpected increase in hurricane forward speed or intensity, evacuation traffic gridlock, accidents/stalled vehicles or rainfall flooding blocking the road ahead, etc. Wind, together with vehicles, will also cause serviceability and bridge fatigue damage issues. The present study will present the framework of wind–vehicle–bridge interaction analysis and its applications, developed in the last decade by the authors' group, focused on the vehicle and bridge safety issues. It consists of the following five parts: (1) A three dimensional finite element analysis framework considering the interaction of wind, bridge and vehicles; (2) experimental facilities development and studies for both static and aerodynamic tests of bridge section models and vehicles; (3) Computation fluid dynamic (CFD) prediction of loading on vehicles; (4) performance evaluation of vehicle safety and bridge fatigue; and (5) bridge vibration mitigations. Case study will also be presented and future research needs are discussed.

Results from 23 cyclic tests, including 18 cantilever-typed steel bridge piers and five beam-to-column connections, are presented to investigate their ductile fracture behavior as related to the seismic design of steel bridge structures, and based on shell and fiber models, two evaluation methods of ductile crack initiation are proposed. The effect of various parameters, including plate width-thickness and column slenderness ratios, cross-section shape, loading history, repeated earthquakes and initial weld defect is investigated experimentally. Among these parameters, width-thickness ratio, loading history and initial weld defect are shown to have significant influence on ductile fracture behavior. The test data suggest that for unstiffened box specimens, current seismic design provision limits on ultimate strain may not provide sufficient ductility for seismic design. On the other hand, based on the experimental results, two damage index-based evaluation methods respectively using shell model and fiber model are successfully employed to predict ductile fracture of steel bridge structures. Comparisons between experimental and analytical results show that they can predict ductile fracture behavior with good accuracy across the specimen geometries, steel types, loading histories and initial weld defects.

P-Δ effect is one of the crucial reasons causing the collapse of structures under strong earthquake excitations. Numerical example shows that the lateral stiffness of structure decreases when the P-Δ effect is considered, and the backbone curve is easy to behave a negative slope when the geometric nonlinearity and the material nonlinearity are combined. A simplified trilinear curve including the elastic range, the yield range and the softening range is used to simulate the characteristic of the backbone curve, and the hysteretic models including the nonlinear elastic model, the full elasto-plastic model and the Clough model are developed. The influence of the hysteretic characteristic on the collapse resistance capacity of the structure is researched by a series of incremental dynamic analysis (IDA) for the single-degree-of-freedom (SDOF) system. The results demonstrate that the collapse resistance capacity of the structure is not always proportional to the energy dissipation capacity, while the biasing movement tendency when the structure goes into the negative stiffness branch is the main reason causing the collapse of the structure.

This paper presents the findings of a research that focused on the seismic performance of masonry-infilled, nonductile, RC frames. This research has resulted in improved analytical methods and effective retrofit techniques to assess and enhance the performance of these structures. The methods were validated by a series of quasi-static tests conducted on one-story frame specimens as well as shake-table tests conducted on two 2/3-scale, three-story, two-bay, masonry-infilled, RC frames. This paper focuses on the observations from the shake-table tests and the further insight gained from a numerical study conducted with finite element models. The first shake-table test specimen had no retrofit measures, and the second had infill walls in the first and second stories strengthened with Engineered Cementitious Composite (ECC) and Fiber Reinforced Polymeric (FRP) overlays, respectively. The tests demonstrated the effectiveness of the retrofit measures. Finite element models that combine smeared and discrete cracks have been used in a numerical study to examine the benefits of the ECC retrofit and the influence of the capacity of the shear dowels that connect an ECC overlay to the RC beams on structural performance. It has been shown that these shear dowels play a critical role in enhancing both the strength and ductility of a retrofitted structure.

The superior human vision system provides ingenious insight into an ideal damage detection strategy in which structural modeling scales are not only spatially varying but also dynamically changed according to actual needs. This paper experimentally examines the efficacy of a multi-scale damage detection method based on wavelet finite element model (WFEM). The beam-type wavelet finite element in this study utilizes the second-generation cubic Hermite multi-wavelets as interpolation functions. The dynamic testing results of a one-bay steel portal frame with multiple damages are employed in the experimental validation. Through a multi-stage updating of the WFEM, the multiple damages in the steel portal frame are detected in a progressive manner: the suspected region is first identified using a low-scale structural model, and the more accurate location and severity of the damage can be identified using a multi-scale model with local refinement. As the multi-scale WFEM considerably facilitates the adaptive change of modeling scales, the proposed multi-scale damage detection method can efficiently locate and quantify damage with minimal computation effort and a limited number of updating parameters and sensors, compared with conventional finite element methods.

A family of simulation methods for nonstationary earthquake ground motions is proposed. It employs a univariate model of phase spectrum built up on a time argument associated with the concept of starting-time of phase evolution of frequency components. This phase model allows a feasible phase spectrum just using few variables of the starting-time in numerical implementation. In order to reduce the computational effort of the starting-time, a wave-group propagation formulation is also introduced. Two observed ground motions at the type-II site, i.e. Northridge and Chi-Chi waves, are investigated for illustrative purposes. Inspired from the proposed method, a numerical technique for the spatial variation of ground motions is also developed, and the investigation of coherency function between the example ground motions observed at different stations is carried out. Numerical results prove the validity and applicability of the simulation scheme. This methodology provides a new perspective towards the representation of nonstationary stochastic ground motions.

Located between the Eurasia seismic zone and the circum-Pacific seismic belt, China is the largest continent shallow earthquake area around the world by the frequent earthquake activities. And great quantities of tunnels are located in high earthquake intensity area of China. As one of the main structure of the national lifeline, the seismic analysis methods of tunnel must be paid high attention. Based on seismic response characteristics of the traffic tunnel structure, this paper provides a synthesis of the current state of knowledge in the area of seismic analysis for tunnel, including the seismic design criteria, earthquake effects, tunnel seismic behaviors, and the seismic analysis procedure of tunnel. It focuses on analysis methods of tunnel subjected to seismic motion. There are three major seismic analysis methods normally used in tunnel structures; they are seismic coefficient method, seismic deformation method and dynamic response method. The basic principles of the three methods are described in this paper. Based on the different mechanical characteristics between cross-section and axial direction, the proper seismic analysis methods in the two directions are put forward according to the different construction method of tunnel. The research results will provide reference for seismic analysis of traffic tunnel.

A new rate-dependent stochastic damage model for the dynamic modeling of concrete is presented in the paper. This model is formulated on the basis of the stochastic damage model, from which, the static stochastic evolution of damage is strictly derived. Then, rate dependency of concrete is included by means of viscous-damage mechanism. The model predictions are tested against experimental results on concrete specimens that cover different strain rates. The results demonstrate the proposed model may predict dynamic failure behavior of concrete quite well.

In this paper, a mesoscale model is adopted to simulate concrete behavior under dynamic split tension. The concrete material is assumed to comprise coarse aggregates, mortar matrix, and an interfacial transition zone (ITZ). In the mesh generation process, random coarse aggregate particles are generated from a certain aggregate size distribution and then placed into the mortar matrix with ITZ between the coarse aggregate edge and the mortar matrix. Different aggregate shapes, such as circular, oval, and polygons are modeled to analyze the gravel and crushed stone aggregates. Numerical simulation is used to model the dynamic damage responses of a typical cylinder concrete specimen and a cube specimen under split tension. Velocity boundary is added as the dynamic loading. Reasonable tensile stress–strain relationships are obtained at the macroscale level; and the detailed stress wave distribution and the crack pattern are obtained at the mesoscale level. These numerical results agree well with conventional experimental results. It also shows that cracks are affected by aggregate distribution.

This paper seeks to develop a module for automated model construction of a pipeline network using geographical information system (GIS) of lifeline, for the sake of more rational seismic disaster assessment. The module is assigned a functionality which enables to generate two types of analysis models, a simple 2D model and a 3D model with high fidelity for pipe configuration. The module is coded in an objective oriented programming, so that it is easier to be extended to generate other types of analysis models. The module is applied to actual GIS, and the configuration of the generated model is verified. As an example, numerical analysis is made for the automatically constructed models by using a commercial finite element method package, and it is shown that these models are mechanically consistent and can be used for seismic disaster assessment.