Robust Design of a Single Tuned Mass Damper for Controlling Torsional Response of Asymmetric-Plan Systems

A new robust design methodology to control the seismic performance of asymmetric structures equipped with a Single Tuned Mass Damper (STMD) is presented in this article. This design approach aims to control the seismic response of such systems by reducing both flexible-and stiff-edge maximum displacement. The dynamic problem has been investigated in the state space representation showing that the TMD works as a closed-loop feedback control action. A synthetic index to estimate the seismic performance of the main system has been defined by using H_∞ norm. Wide-ranging parametric numerical experimentation has been carried out to obtain design formulae for the STMD in order to minimize such a performance index. These formulae allow for a simple design of STMD position and stiffness to optimally control both translational and rotational motion components, whereas two mass devices are generally considered to improve the seismic performance of asymmetric structural systems The effectiveness and efficiency of the obtained design formulae have been tested by investigating the dynamic behavior of the asymmetric structure after being subjected to different recorded seismic inputs.     

The Influence of Masonry Infill Walls in the Framework of the Performance-Based Design

In this article, a performance-based seismic design (PBD) methodology is proposed for the design of reinforced concrete buildings, taking into account the influence of infill walls. Two variants of the PBD framework are examined: The first is based on the non-linear static analysis procedure (NSP) while the second relies on the non-linear dynamic analysis procedure (NDP). Both design approaches are compared in the context of structural optimization with reference to the best possible design achieved for each case examined. Life-cycle cost analysis is considered a reliable tool for assessing the performance of structural systems and it is employed in this study for assessing the optimum designs obtained. The optimization part of the problem is performed with an Evolutionary Algorithm while three performance objectives are implemented in all formulations of the design procedures. The two most important findings can be summarized as follows: (i) if structural realization follows the design assumptions, then total expected life-cycle cost of the three type of structures, bare, fully infilled and open ground story, is almost the same and (ii) if an open ground story building is designed as bare or as fully infilled frame, real performance will be much worse than anticipated at the design stage.     

General Seismic Load Distribution for Optimum Performance-Based Design of Shear-Buildings

An optimization method based on uniform damage distribution is used to find optimum design load distribution for seismic design of regular and irregular shear-buildings to achieve minimum structural damage. By using 75 synthetic spectrum-compatible earthquakes, optimum design load distributions are obtained for different performance targets, dynamic characteristics, and site soil classifications. For the same structural weight, optimum designed buildings experience up to 40% less global damage compared to code-based designed buildings. A new general load distribution equation is presented for optimum performance-based seismic design of structures which leads to a more efficient use of structural materials and better seismic performance.     

MOMENT RESISTING WELDED CONNECTIONS: AN EXTENSIVE REVIEW OF DESIGN PRACTICE AND EXPERIMENTAL RESEARCH IN USA,JAPAN AND EUROPE

Welded connections, widely used in seismic moment resisting frames (MRFs) in USA, Japan and Europe, have been extensively investigated during the 1990s in order to improve their performance under severe earthquakes. In order to correctly evaluate the results of experimental research on welded connections, the differences among the American, Japanese and European current practices in designing the frame structural systems and in detailing the beam-to-column connections should be firstly appraised. In this paper, the major aspects characterising the USA, Japan and Europe design practice in moment resisting welded connections are reported, the differences are underlined and the main issues recently addressed in experimental research are reviewed. Among the several parameters which affect the connection performance, attention is focused on the effect of the beam cross-section size. Thus conclusions are drawn in terms of plastic rotation capacity as dependant on the beam size.     

南京六朝建康都城城墙夯土遗址锚杆加固技术研究

为了对南京六朝建康都城城墙夯土遗址进行科学保护,确保遗址展示面的结构安全,首先通过ANSYS有限元模拟对城墙夯土遗址的现状及锚杆加固后的结构性能进行研究,分析包括锚杆长度、锚杆角度、锚杆弹模、锚杆直径、边坡坡度、锚杆间距、土体含水率等参数对遗址安全性的影响,得出不同参数变化下的夯土遗址结构的安全系数,给出了适合夯土遗址锚杆加固的优选技术参数。为了验证理论计算的准确性以及锚杆和灌浆材料施工的可行性,进行了锚杆和灌浆材料的拉拔试验。最后,结合理论分析和试验研究结果,提出了采用不锈钢锚杆和改性泥浆灌浆的方法进行遗址锚杆加固的设计方案。该城墙夯土遗址锚杆加固技术研究的成功,可为类似文物保护设计分析提供参考。     

故宫灵沼轩残损分析及结构性能研究

故宫灵沼轩是我国最早建造的钢铁-砌体组合结构之一,目前损坏较为严重。为更好地保护和修缮该建筑,残损分析和结构性能研究是其修缮保护的科学基础。首先通过现场调研,对该建筑的残损状况进行分析,找出其显见的病害;然后通过精确测绘、材料检测及有限元模拟分析其结构性能,找出其隐在的病害;最后综合残损分析及结构性能分析结果,提出相应的保护措施建议。     

AUTOMATIC MINIMIZATION OF THE RIGIDITY ECCENTRICITY OF 3D REINFORCED CONCRETE BUILDINGS

The objective of this paper is to obtain the optimum design of 3D reinforced concrete buildings in terms of their performance under earthquake loading. This goal is achieved by considering the minimisation of the eccentricity between the mass centre and the rigidity centre of each storey layout as the optimisation objective in order to produce torsionally balanced structures. This problem is considered as a combined topology and sizing optimisation problem. The location and the size of the columns and the shear walls of the structure of each storey layout constitute the design variables. Apart from the constraints imposed by the seismic and reinforced concrete structure design codes, architectural restrictions are also taken into account. The test examples showed that a reduction in the structural cost of the building is achieved by minimising the eccentricity between the mass centre and the rigidity centre of each storey layout. Evolutionary optimisation algorithms and in particular a specially tailored algorithm based on Evolution Strategies is implemented for the solution of this type of structural optimisation problems.     

Behavior Factor for Performance-Based Seismic Design of Plane Steel Moment Resisting Frames

Simplified expressions to estimate the behavior factor of plane steel moment resisting frames are proposed, based on statistical analysis of the results of thousands of nonlinear dynamic analyses. The influence on this factor of specific structural parameters, such as the number of stories, the number of bays, and the capacity design factor of a steel frame, is studied in detail. The proposed factor describes the seismic strength requirements in order to restrict maximum storey ductility to a predefined value. Interrelation studies between maximum storey ductility and the Park-Ang damage index are also provided for the damage-based interpretation of the performance levels under consideration. Realistic design examples serve to demonstrate the ability of the proposed factor to convert conventional force-based design to a direct performance-based seismic design procedure.     

Use of Cumulative Ductility Spectra Within a Deformation-Control Format for Seismic Design of Ductile Structures Subjected to Long Duration Motions

Due to the large economical losses derived from recent seismic events, design methodologies that are based in the explicit control of the dynamic response of structures have been formulated. This article introduces, within the framework of performance-based design, a numerical methodology for the seismic design of structures that are expected to undergo severe cumulative plastic demands. The methodology explicitly considers and integrates: (1) the structural and non-structural performance of the building; (2) the life safety limit state; and (3) the prevention of low cycle fatigue.     

Robust Performance-Based Design Optimization of Steel Moment Resisting Frames

The concept of performance-based design is considered in the framework of Robust Design Optimization (RDO) for the design of steel structures. The RDO problem is treated as a two-objective optimization problem where the initial construction cost and the variance of the maximum interstorey drift for the 10% in 50 years hazard level are considered as the problem objectives to be minimized. The structural performance is evaluated by means of the reliability demand and resistance methodology of the FEMA-350 guidelines in order to take into account both uncertainty and randomness in a consistent manner. The structure is designed to respond for different levels of seismic hazard levels with a desired confidence. The limit-state damage cost is used as a measure for the assessment of selected designs that have been obtained through the proposed RDO formulation. The non deterministic finite element problem encountered, is solved using the Monte Carlo Simulation method. The NSGA-II algorithm has been combined with the Evolution Strategies optimization algorithm for solving the two-objective optimization problem at hand.     

Seismic Performance Assessment of Slender T-Shaped Reinforced Concrete Walls

T-shaped slender reinforced concrete (RC) structural walls are commonly used in medium-rise and high-rise buildings as part of lateral force resisting system. Compared to its popularity, experimental results on seismic performance of these walls are relatively sparse, especially for data regarding these walls in the non-principal bending directions. This article aims at providing additional experimental evidence on seismic performance of T-shaped RC structural walls. Experimental results of six T-shaped RC walls were presented. These walls resemble the structural walls found in existing buildings in Singapore and possess slightly inferior details compared to the requirements of modern design codes. The test variables were the loading direction and the axial load ratio. The experimental results were discussed in terms of the failure mechanisms, cracking patterns, hysteretic responses, curvature distributions, displacement components, and strain profiles. In addition, the experimental results were compared with methods commonly adopted in current design practice including the nonlinear section analyses, shear strength models and effective width of the tension flange. The experimental data illustrate that the shear lag effect not only was not accurately accounted for by the effective width method but also significantly affected the strength and stiffness of the tested specimens.     

Seismic Performance of Tuned Liquid Column Dampers for Structural Control Using Real-Time Hybrid Simulation

This article presents real-time hybrid simulation (RTHS) in a single-degree-of-freedom (SDOF) steel frame incorporated with tuned liquid column damper (TLCD). The SDOF steel frame is numerically simulated, and the TLCD alone is physically experimented on a shaking table. The delay-dependent stability of RTHS system for TLCD investigation is first assessed; and the delay-dependent accuracy is verified by comparing the responses obtained through the RTHS, the conventional shaking table test, and an analytical solution. Then, RTHSs are carried out to evaluate the effects of mass ratio, structural damping ratio, structural stiffness, and peak ground acceleration on the reduction effectiveness of STLCD. The nonlinear behavior of the STLCD is experimentally captured. Finally, the structural responses under STLCD and multiple TLCDs (MTLCD) control are compared. It is found that the performance of STLCD strongly depends on structural parameters and properties of earthquakes; both MTLCD and STLCD induce approximately the same response reductions, and the former can enhance the control performance in certain cases. These results presented here may contribute to improve the design and application of TLCDs in practical engineering.     

A Simplified Procedure to Select a Suitable Retrofit Strategy for Existing RC Buildings Using Pushover Analysis

Over the past ten years, the development of analytical procedures to accurately evaluate the seismic performance of existing buildings has gathered the attention of researchers. This has resulted in the publication of several standards, which, however, inadequately cover the issue of retrofit strategy selection. In the present article, a procedure that allows a comparison of available strategies in order to select the optimum solution for an existing deficient building is proposed. The procedure is based on calculating the pushover curve for the unstrengthened structure. A capacity spectrum is then estimated assuming different retrofit scenarios, which is then used for the evaluation of the strategies. The latter is based on criteria that assess the main structural system characteristics and how each solution benefits them. The final step of the procedure introduces simplified rules that allow the approximate design of each retrofit solution, which allows the evaluation of their applicability. The proposed procedure was applied to two idealized buildings with different structural systems. Results obtained indicate that less effective or inapplicable rehabilitation strategies were properly detected. Thus, the results were considered acceptable in terms of identifying the possible optimum strategy, which, however, should be verified with a detailed design of the retrofit system.     

Shaking Table Testing of a Full-Scale Prefabricated Three-Story Timber-Frame Building

Shake table tests were carried out on a 7 m × 5 m three-story, timber light-frame building (7.5 m height) at the TreesLab laboratory (Eucentre) in Pavia. The aim of the research was to evaluate the seismic behavior of a typical Italian prefabricated timber building and to study the interaction between the individual structural components tested in quasi-static manner in a previous experimental study. The 1979 Montenegro Earthquake ground motion, recorded at the Ulcinj-Hotel Albatros station, was selected as the ground motion for seismic tests. The maximum peak ground acceleration was scaled to 0.07 g, 0.27 g, 0.5 g. 0.7 g, and 1 g in order to evaluate the building’s performance at different levels of seismic input. More than 100 instruments were used to monitor the behavior of the building during seismic tests measuring acceleration, displacement, and forces. The visual inspection shows that the building did not show any damage during all seismic tests. However the data analysis (dynamic identification, capacity spectrum, inter-story drift) confirm that during the 1.00 g test the structure went beyond its linear elastic limit. The results obtained from this experimental study suggest that the design hypotheses commonly adopted in practice for seismic analysis (e.g., in terms of force distributions between the walls, and also the behavior factor q) are not always consistent with the real behavior of timber frame multi-story buildings, and should be backed by more accurate knowledge of the contributions of the individual structural components.     

Friction Model for Sliding Bearings under Seismic Excitation

In this article, an experimentally validated model is proposed in order to take into account main sources of performance degradation that could be experienced by friction-based devices during a seismic event. Particular attention is dedicated to the degradation of friction characteristics due to repetition of cycles and consequent temperature rise. This effect can be responsible for overestimate of the dissipation capacity of the device. The proposed model of frictional behavior is suitable for immediate implementation in generalized structural analysis codes and provides an important design tool for realistic assessment of the seismic response of structures equipped with friction-based isolators.     

Modeling and Seismic Response Analysis of Italian Code-Conforming Single-Storey Steel Buildings

ABSTRACT

This article describes the structural design, nonlinear modeling, and seismic analysis of prototype single-storey non-residential steel buildings made of moment-resisting portal frames in the transverse direction and concentric braces in the longitudinal direction. Various design parameters (building geometry, seismic hazard, foundation soil category) and different modeling assumptions (bare frame model, model including cladding elements, ground motions including vertical accelerations, and modeling uncertainties) were considered to investigate their effects on the simulated seismic performance.     

DIAPHRAGM ACTION OF SANDWICH PANELS IN PIN-JOINTED STEEL STRUCTURES: A SEISMIC STUDY

The paper focuses on the seismic response of steel pin-jointed frames braced by lightweight cladding panels. In particular, with the aim to investigate the performance of such a structural scheme when acting as a dissipative system, a wide numerical study has been developed. It is based upon available shear tests on screwed sandwich panels, whose experimental cyclic responses are properly incorporated into a scope-oriented, computer program. The goal is firstly to check the possibility of using cladding panels as shear diaphragms in seismic areas and then to assess an appropriate design behaviour factor, accounting for their actual hysteretic response. Key findings from the nonlinear dynamic analyses are: (1) a portal frame steel building in a low-medium seismicity zone may be braced by common cladding panels, completely avoiding the use of other bracing systems; (2) this structural solution, if compared with a conventional one, appears to be more efficient and cost-effective, giving rise to a weight saving which, in the case under examination, reaches a value of about 20%; (3) on the basis of the numerical study a design behaviour factor q _d =2 seems to be realistic for such a structural typology.     

Seismic Design and Response of Framed Structures with Stiffening Bracing Systems

Stiffening Bracing System (SBS) is proposed as an alternative to conventional braced frames. SBS is intended to reduce the floor accelerations while maintaining uniform inter-story drift along the building height. The system ensures that additional damping devices distributed over the building’s height work efficiently. An iterative design procedure is developed to maintain a desired target performance. The procedure accounts for higher mode effects and supplemental damping. A series of nonlinear response history analyses on braced frames with various heights demonstrated the adequacy of the proposed procedure in achieving target structural performance and seismic demand prediction.     

Seismic Performance and Modeling of a Half-Scale Base-Isolated Wood Frame Building

The concept of base isolation is a century old, but application to civil engineering structures has only occurred over the last several decades. Application to light-frame wood buildings in North America has been virtually non existent with one notable exception. This article quantitatively examines issues associated with application of base isolation in light-frame wood building systems including: (1) constructability issues related to ensuring sufficient in-plane floor diaphragm stiffness to transfer shear from the superstructure to the isolation system; (2) evaluation of experimental seismic performance of a half-scale base-isolated light-frame wood building; and (3) development of a displacement–based seismic design method and numerical model and their comparison with experimental results. The results of the study demonstrate that friction pendulum system (FPS) bearings offer a technically viable passive seismic protection system for light-frame wood buildings in high seismic zones. Specifically, the amount and method of stiffening the floor diaphragm is not unreasonable, given that the inter-story drift and accelerations at the upper level of the tested building were very low, thus resulting in the expectation of virtually no structural, non structural, or contents damage in low-rise wood frame buildings. The nonlinear dynamic model was able to replicate both the isolation layer and superstructure movement with good accuracy. The displacement-based design method was proven to be a viable tool to estimate the inter-story drift of the superstructure. These tools further underscore the potential of applying base isolation systems for application to North America's largest building type.     

A New Proposed Passive Mega-Sub Controlled Structure and Response Control

It is still a serious challenge for structural engineers to effectively reduce the seismic responses of tall and super tall buildings to further improve these structural safeties. In order to solve this problem, in this article a new kind of structural configuration, named passive mega-sub controlled structure (PMSCS), is presented, which is constructed by applying the structural control principle into structural configuration itself, to form a new structure with obvious response self-control ability, instead of employing the conventional method. In the analysis of PMSCS the equations of motion of the seismically excited system are developed, based on a realistic analytical model of the complete mega-structural system. Expressions of the displacement and acceleration response of the structure, resulting from simulated earthquake ground motions represented by stationary and nonstationary random processes, are derived. These responses are then determined for both the PMSCS and its conventional mega-sub structure (MSS) counterpart, whose configuration was modeled after the traditional mega-frame that was used in the construction of the Tokyo City Hall. A parametric study of the structural characteristics that influence the response control effectiveness of the PMSCS is presented and discussed. The region over which these structural characteristics yield the optimum seismic response control of the PMSCS is identified and serves as a very useful design tool for practitioners. The study illustrates that the proposed PMSCS offers an effective means of controlling the seismic displacement and acceleration response of tall/super-tall mega-systems. It also overcomes shortcomings exhibited in earlier proposed mega-sub controlled structural configurations.