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An innovative self-centering hybrid rocking braced steel frame (SCHRBF) with separate braced span and rocking span is proposed for improving seismic resilience. The braced span utilizes buckling-restrained braces (BRBs) to provide energy-dissipating capacity, and the rocking span consists of stiff rocking cores and self-centering braces (SCBs) to achieve a uniform inter-story drift distribution and low post-earthquake residual displacement under a strong earthquake. This study first describes the basic composition and nonlinear mechanical behavior of this novel system. Then, a force-based seismic design procedure for the SCHRBF system is proposed, including the determination and allocation of base shear, design of BRBs in braced span, design of SCBs in rocking span, and design of rocking core members. The influence of key design parameters on the seismic responses of the system is then explored through parametric analysis. And recommended values of the design parameters are provided according to the analysis results. Although the properly designed structure has significant partial re-centering behavior, its peak inter-story drifts, residual inter-story drifts, and deformation patterns can be effectively controlled under strong earthquakes. Finally, the superiority of the SCHRBF in controlling seismic displacement responses is verified by comparing with other structural systems.

During the mid 1990s earthquakes in Northridge, California, and Kobe, Japan, illustrated a lack of understanding of the behaviour of structural steels exposed to seismic loads. Under this type of load regime, structural steel members are subjected to fully plastic load cycles and unexpectedly brittle failures may result.

A method for determining the accumulation of damage through cyclic pre-straining is proposed. Toughness, as defined by the area under the true stress strain curve, is used as an indicator of the level of damage that the steel has suffered and from this some idea of its remaining capacity to further deform can be determined.

Observations during the testing of these samples have indicated that there is a transition in the failure mode from a fatigue type failure, with a progressively growing crack, to an overload failure, in which the steel fails due to a lack of ability to further deform. Similar transitions have been noted by other researchers in the field. Analysis of the test results seems to show differences in the damage accumulation behaviour that may be used to identify when this transition in failure modes may occur.

The currently-used AASHTO seismic design code for continuous plate-girder bridges built in areas of low to moderate seismicity is evaluated. The seismic behavior of a typical plate-girder bridge, designed according to the code, is studied in detail using a linear time-history analysis, and the peak response values of important parameters are computed. The effects of vertical ground excitation, seismic wave propagation, and change in support conditions on the bridge seismic response are investigated. The results are compared with those obtained using the current AASHTO seismic design code. The study concludes that the effect of vertical ground excitation on the plate-girder bending moments could be significant. It was found that the effect of seismic wave propagation on bending moments and shear forces in the bridge piers should be considered in the analysis of continuous plate girder bridges with several immovable supports when built in zones of low wave propagation speeds (e.g. 244 to 488 m/s). The study further concludes that AASHTO single mode spectral analysis slightly underestimates the forces in the bridge piers.

This paper deals with the dynamics of a single-degree-of-freedom elastoplastic oscillator. The model adopted herein is useful for understanding the dynamic behavior of civil engineering structures, such as steel structures, especially when plastic inelasticity is of concern. Using appropriate internal variables, the dynamic hysteretic system can be written as a singular autonomous system. The free vibration of such a nonlinear system reduces to periodic motion. The harmonic forced oscillator can exhibit periodic or quasi-periodic behaviors. A bifurcation diagram is numerically computed, which indicates that periodic elastoplastic limit cycles exist for some ranges of structural parameters. The bifurcation boundary separates the shakedown from other alternating plasticity phenomena.

The buckling-restrained braces (BRBs) are widely applied in reinforced concrete frames (RCFs) to improve their performance under seismic loading. A procedure for designing such structures based on stiffness ratios was developed. The stiffness ratio was assumed to decrease gradually from the bottom story to the roof. The intermediate stiffness ratios were defined by linear interpolation. A step-by-step design procedure was presented. Three structures with 5, 10, and 15 stories were designed using the procedure and considering three seismic intensity levels. Linear time analysis showed that the stiffness ratio reduced along structural height had no significant effect on the inter-story drift ratio (IDR) of low-rise structures. The nonlinear time history analysis was performed to assess the structural seismic performance. On the basis of the analytical results in terms of the elastic and inelastic IDRs, reinforcements, hysteretic energy ratios of BRBs and structural damage, recommended range of stiffness ratios are proposed for various structures and design seismic intensities.

The safety of railway vehicles running on bridges needs to be evaluated in the seismic design of bridges. This study examined the spectral intensity calculated from the lateral vibration of the bridge deck during earthquakes, a Japanese code-based index to measure bridge vibration’s strength. In addition, the effect of the torsion of the bridge deck on vehicle derailment is investigated using a nonlinear vehicle–track–bridge model. The bridge deck torsion increases the derailment risk, especially for bridges with a low natural frequency. The reason lies in that the lateral and torsional deck motions are highly correlated for bridges with lower frequency. Based on this observation, a code-type formula was proposed to evaluate the vehicle running safety including both lateral and torsional motions of the bridge deck. The accuracy of the proposed formula was demonstrated by comparison with vehicle–track–bridge simulation excited by ground motion records. The new procedure overcomes the non-conservative assessment of derailment caused by ignoring bridge torsion.

This paper proposes a novel intensity measure (IM) based on the geometric mean of acceleration response spectral ordinates to assess the probabilistic performance of structures subjected to seismic loading. Instead of relying solely on the fundamental period, the proposed IM is evaluated across a fixed period range for all structural systems, which allows consideration of higher mode effects and period changes due to nonlinearity. The proposed seismic IM is evaluated using two established indices sufficiency and efficiency. Sufficiency quantifies the independence of an engineering demand parameter at a specific intensity level with ground motion characteristics such as seismic magnitude $(M)$ and distance from site to fault plane $(R)$. It is calculated by linear regression analysis, or using gradient-based relative sufficiency measures. On the other hand, efficiency is measured as dispersion across ground motions at a given intensity level for any physical response quantity. It helps to reduce computational demand for failure probability assessment by considering a smaller number of records compared to an inefficient IM for similar confidence levels. The effectiveness of the proposed IM along with 10 other IMs is demonstrated on single degree of freedom systems with various fundamental periods by performing nonlinear time history analysis using a far-field ground motion record set. The study is also extended to five degree of freedom lumped mass stick models, 2D models (4-, 8-, and 12-story archetype steel frames), and 3D reinforced concrete shear wall building model. The results indicate that the proposed IM limits dispersion to within 10% for long-time period structures, and demonstrates improved sufficiency across different structural systems. For example, gradient of the proposed IM with respect to magnitude $M$ and site-to-source distance $R$ for a 12-story steel frame is reduced by 42.9% and 94%, respectively, compared to spectral acceleration at fundamental time period. Potential application of this research lies in efficiently conducting seismic reliability assessment and design for structural systems.

The purpose of this study is to compare the site effect section of building codes (EC8 and UBC97) with the set of data provided by the Kyoshin network. In order to obtain a set of site coefficients and spectral shapes, we have first deduced an attenuation law for both horizontal and vertical motion. Site conditions are represented by the shear velocity averaged over the upper 30 m . Our site classification (4 categories similar to those proposed in the new EC8 and the UBC97) is based on borehole investigations at every station. This classification has permitted to distinguish clearly four response spectra which demonstrates the efficiency of as characterising site conditions. Our law is then used to test site coefficients and spectral shapes of building codes EC8 and UBC97. Concerning spectral shapes and site coefficients, our results are found to be in good agreement with EC8 and UBC97 only if category B is taken as reference. We also conclude that a site which is characterised as "rock" on geological criteria can not generally be classified in category A . This suggests that classification in category A should be based only on field measurements. Concerning vertical motion, our analysis of the K-NET data shows that the ratio av/ah (vertical peak ground acceleration over horizontal peak ground acceleration) is between 0.50 and 0.68.

A large number of multi-storey reinforced concrete frame buildings with masonry infill walls, which were uniformly distributed over the height of the building, collapsed in the 1999 Kocaeli (Turkey) earthquake, due to complete failure of the first storey or the bottom two stories. In the paper it is demonstrated that a soft storey mechanism is formed in such structural systems if the intensity of ground motion is above a certain level. It is likely that collapse will occur if the global ductilities of the bare frames, as well as the ductilities of the structural elements, are low, and if the infill walls are relatively weak and brittle.

The author got a chance to visit Turkey for investigating the damage of industrial facilities in the 1999 Kocaeli Earthquake which occurred on 17 August 1999 in the Kocaeli province of Turkey.

This report provides a brief investigation obtained through the seismic damage survey, particularly, focused on the damages to industrial facilities. The epicentral area in the Kocaeli province is the most industrial region of Turkey. Severe excitation attacked this region and industrial plants and structures were more or less damaged. Since the author could only visit a few sites, the report mainly describes the damages of two plants; TÜPRAŞ oil refinery where big fire occurred and TOYOTA–SA car manufacturing factory where no significant damage appeared.

The core of the paper consists of the illustration of a method for seismic reliability analysis of non-linear structures. The method, which is a development over a recent previous proposal, is quite comprehensive in scope since it includes consideration of randomness in the input, in the mechanical properties of the structure and in the limit-state, or capacity, conditions. Essentially, the problem is formulated as the out-crossing of the response process out of a (scalar) safe threshold, and this problem is solved by time-invariant FORM methods. An application to an idealised five-storey building demonstrates the salient theoretical and computational features of the method. The new approach is presented in a broader framework, which involves a discussion on present trends and capabilities in the area of probabilistic seismic design. For the sake of this discussion, two approaches just appeared in the literature are outlined, which are less demanding from a theoretical standpoint, and hence closer to engineering practice, but also less general in scope. It is argued that their introduction on code-assisted design would be feasible immediately with obvious advantages, while approaches of more rigorous nature would be given some more time to mature and to become more accessible to professional use.

This paper presents the concept of constant strength design spectra for the design of base-isolated structures; particularly those structures using isolators with a bilinear hysteretic behaviour when subjected to dynamic loading. The constant strength design spectra relate peak accelerations, velocities, displacements and effective isolated natural periods for bilinear systems with a given yield strength and post yield stiffness. Constant strength design spectra could be useful for the design of base isolators with bilinear hysteretic behaviour, as these devices can be designed for fixed yield strength and post yield stiffness. The concept of constant strength design spectra and its application for the design of base isolated structures is illustrated with case studies of specific structures.

Displacement based design (DBD) methods are emerging as the latest tool for performance based seismic design. Of the many different DBD procedures proposed in recent years there are few that are developed to a standard suitable for implementation in modern design codes. This paper presents the findings of a study that uses eight different DBD methods to undertake the seismic design of five different case studies. Some significant limitations with the eight methods have been identified through their application to realistic design examples. The study also shows that despite all of the DBD methods using the same set of design parameters, a large variation in design strength is obtained. Finally, through non-linear time history analyses the performance of each method is assessed. The performance assessment indicates that each of the eight DBD methods provide designs that ensure limit states are not exceeded. It is hoped that by presenting the limitations and comparing the required strength and performance of the methods, developments will be made that will enable designers to undertake DBD with ease and confidence.

Welded connections are extensively used by the precast concrete industry to ease construction. When the seismic resistance and ductility of a building incorporating precast concrete elements needs to be assured, the connections should be carefully designed and constructed to avoid undesirable structural performance. This paper discusses aspects related to an analytical and experimental programme conducted to investigate the response of a connection detail for coupling precast concrete walls in low to medium rise buildings. The connection consists of a rectangular steel plate with a concentric circular perforation. In this way, a weak but ductile link is introduced in the system. Using the principles of capacity design, the walls can be designed as if coupled and with energy dissipation taking place in the connection. Simplified expressions are presented to evaluate the shear stiffness and the yield and ultimate strength of the perforated steel plates, based on theory and the experimental data collected during the test.

The present study deals with the seismic performance of partial perimeter and spatial moment resisting frames (MRFs) for low-to-medium rise buildings. It seeks to establish perimeter configuration systems and hence the lack of redundancy can detrimentally affect the seismic response of framed buildings. The paper tackles this key issue by comparing the performance of a set of perimeter and spatial MRFs, which were "consistently designed". The starting point is the set of low- (three-storey) and medium-rise (nine-storey) perimeter frames designed within the SAC Steel Project for the Los Angeles, Seattle and Boston seismic zones. Extensive design analyses (static and multi-modal) of the perimeter frame buildings and consistent design of spatial frame systems, as an alternative to the perimeter configuration, were conducted within this analytical study. The objectives of the consistent design are two-fold, i.e. obtaining fundamental periods similar to those of the perimeter frames, i.e. same lateral stiffness under design horizontal loads, and supplying similar yield strength. The seismic behaviour of perimeter and spatial configuration structures was evaluated by means of push-over non-linear static analyses and inelastic dynamic analyses (non linear time histories). Comparisons between analysis results were developed in a well defined framework since a clear scheme to define and evaluate relevant limit states is suggested. The failure modes, either local or global, were computed and correlated to design choices, particularly those concerning the strength requirements (column overstrength factors) and stiffness (elastic stability indexes). The inelastic response exhibited by the sample MRFs under severe ground motions was assessed in a detailed fashion. Conclusions are drawn in terms of local and global performance, namely global and inter-storey drifts, beam and column plastic rotations, hysteretic energy. The finding is that the seismic response of perimeter and spatial MRFs is fairly similar. Therefore, an equivalent behaviour between the two configurations can be obtained if the design is "consistent".

A five-storey steel frame incorporating dissipative knee elements is designed using the Eurocode 8 pushover analysis method. The non-linear analysis makes use of a novel knee element model capable of accurately simulating the bending and shear behaviour observed in full-scale tests. The performance of the structure is assessed using non-linear time-history analysis. This shows that the knee elements can be designed to yield under small earthquakes or early in a strong one (maximising their energy dissipation) while still being able to withstand a large event without collapse. Knee elements thus have the potential to give excellent seismic performance in steel framed structures. The time history analysis results are compared to those obtained with the three different pushover analysis methods (Eurocode 8, FEMA 356 and ATC 40). The FEMA 356 method, which includes a more accurate representation of the structure's significant post-yield stiffness, gave the closest agreement with the time history analyses, while the Eurocode 8 method gave rather conservative results and the ATC 40 method appears non-conservative for this type of structure.

Classification of earthquake strong ground motion (SGM) records is performed using fuzzy pattern recognition to exploit knowledge in the data that is utilised in a genetic algorithm (GA) search and scaling program. SGM records are historically treated as "fingerprints" of certain event magnitude and mechanism of faulting systems recorded at different distances on different soil types. Therefore, databases of SGM records of today present data of complex nature in high dimensions (many of the dimensions — or SGM parameters in time and frequency domain — are presently available from different archives). In this study, simple ground motion parameters were used but were combined and scaled nonlinearly such that the physical properties of the data could be preserved while reducing its dimensionality. The processed data was then analysed using fuzzy c-means (FCM) clustering method to explore the possibility of meaningfully representing earthquake SGM data in lower dimensions through finding subsets of mathematically similar vectors in a benchmark database. This representation can be used in practical applications and has a direct influence on the processes of synthesising ground motion records, identifying unknown ground motion parameters (e.g. soil type in this study), improving the quality of matching SGM records to design target spectra, and in rule generalisation for response. The results showed that the stochastic behaviour of earthquake ground motion records can be accurately simplified by having only a few of motion parameters. The very same parameters may also be utilised to derive unknown characteristics of the motion when the classification task on "training" records is performed carefully. The clusters are valid and stable in time and frequency domain and are meaningful even with respect to seismological features that were not included in the classification task.

Experimental and numerical simulations are performed to evaluate the modification of ground response resulting from either the presence of soft layers or occurrence of partial liquefaction. Results from two densely instrumented dynamic centrifuge tests are presented to show the ambiguous role played by the presence of a soft layer. It was found that the lateral extent of the soft layer has significant influence on the overall response of the layered strata and any structure founded on it. The experimental observations are supported by simplified numerical analysis. The amplification or deamplification of the input motion is found to be a function of the ratio of the width of soft layer to the wave length. Based on the numerical analysis, a general function describing the site amplification is presented which may be used as a guide in seismic design of foundations in such layered strata.

A displacement-based design (DBD) methodology for structures that are comprised of both frames and walls has been proposed and then tested through examination of several case studies. Strength proportions between walls and frames are decided before any analysis has begun. The various steps required to represent a frame-wall structure as a single-degree of freedom system are identified and a Direct DBD process is then adopted to set the required strength level. To test the design methodology, two sets of 4, 8, 12, 16 and 20-storey reinforced concrete structures are designed, with different proportions of the total strength assigned to the frames. A suite of time-history analyses have then been conducted to validate the methodology, which is seen to perform reasonably well. Finally, improvements to the procedure are outlined and areas for future research are identified.

A direct displacement-based design (DBD) procedure for structures that comprise both frames and walls is presented in this paper. Within the new procedure, strength proportions between walls and frames are assigned and are used to establish the design displacement profile before any analysis has taken place. Knowledge of the displacement profile and recommendations for the combination of frame and wall damping components enables representation of the structure as an equivalent single-degree of freedom system. The Direct DBD process is then utilised to set the required strength level which is proportioned to the structure in line with the initial strength assignments. To test the design methodology, two sets of 4-, 8,- 12-, 16- and 20-storey reinforced concrete structures are designed. The first set considers frame-wall structures in which the frames are parallel to the walls and the second considers structures in which link-beams connect from the frames directly onto the ends of the walls. A suite of time-history analyses are conducted to validate the methodology, which is seen to perform excellently.