Analytical prediction of experimental building pounding

Valuable insights on the problem of seismic pounding have been obtained recently from analytical studies. So far, the proposed analytical models have not been validated experimentally. This paper presents the results of shake table tests of pounding between adjacent three- and eight-storey single-bay steel framed model structures. The pounding response of the frames was measured for various earthquake intensities and initial separations. The experimental results were compared to the predictions resulting from two existing pounding analysis programs. The solution strategy of the first program, SLAM-2, is based on a modal superposition technique. The second program, PC-ANSR, is a non-linear time-step analysis code in which an elastic gap element has been included. Modelling the pounding effect by elastic gap elements in the two programs produced accurate displacement and impact force results. Amplitudes of short acceleration pulses were not well predicted, however, for practical time-step increments. Relative rotations between adjacent floors induced grinding contacts which cannot be captured by uni-axial gap elements.     

Displacement‐based seismic analysis for out‐of‐plane bending of unreinforced masonry walls

This paper addresses the problem of assessing the seismic resistance of brick masonry walls subject to out‐of‐plane bending. A simplified linearized displacement‐based procedure is presented along with recommendations for the selection of an appropriate substitute structure in order to provide the most representative analytical results. A trilinear relationship is used to characterize the real nonlinear force–displacement relationship for unreinforced brick masonry walls. Predictions of the magnitude of support motion required to cause flexural failure of masonry walls using the linearized displacement‐based procedure and quasi‐static analysis procedures are compared with the results of experiments and non‐linear time‐history analyses. The displacement‐based procedure is shown to give significantly better predictions than the force‐based method. Copyright © 2002 John Wiley & Sons, Ltd.     

SEISMIC TESTING OF A BUILDING STRUCTURE WITH A SEMI-ACTIVE FLUID DAMPER CONTROL SYSTEM

This paper describes shaking table tests of a multi-storey scale-model building structure subjected to seismic excitation and controlled by a semi-active fluid damper control system. The semi-active dampers were installed in the lateral bracing of the structure and the mechanical properties of the dampers were modified according to control algorithms which utilized the measured response of the structure. A simplified time-delay compensation method was developed to account for delays within the control system. The results of the shaking table tests are presented and interpreted and analytical predictions are shown to compare reasonably well with the experimental results. © 1997 John Wiley & Sons, Ltd.     

Experimental and analytical studies of structures seismically isolated with an uplift‐restraining friction pendulum system

This paper presents findings from a comprehensive analytical and experimental study on the uplift‐restraining XY‐FP sliding isolation system. To investigate the effectiveness of the XY‐FP isolator and provide a rational basis for evaluating the efficacy of the developed mathematical model, an extensive experimental program was conducted on the earthquake simulator at the University at Buffalo. The experimental program involved a slender, five‐storey, scale‐model frame seismically isolated with four XY‐FP isolators subjected to simulations of historical horizontal and vertical ground motions. The experimental response demonstrates the validity of the concept and provides evidence for the effectiveness of the XY‐FP isolator in preventing uplift. A comprehensive analytical model capable of emulating the mechanical behaviour of the XY‐FP isolator is developed and implemented in program 3D‐BASIS‐ME. The newly enhanced program is used to predict the dynamic response of the seismically‐isolated model structure. Comparison of analytical predictions with experimental results attests to the efficacy of the analytical model for simulating the response of the XY‐FP isolator. With its appealing conceptual simplicity and its proven effectiveness, the new uplift‐restraining isolator has the potential to facilitate the application of seismic isolation even under the most extreme of conditions, including but not limited to near‐fault strong ground motions and uplift‐prone structural systems. Copyright © 2005 John Wiley & Sons, Ltd.     

PERFORMANCE EVALUATION OF A THREE-STOREY UNREINFORCED MASONRY BUILDING DURING THE 1992 ERZİNCAN EARTHQUAKE

Seismic performance of a three-storey unreinforced masonry building which survived the 1992 Erzincan earthquake without damage is evaluated. Mechanical properties of the masonry walls have been determined experimentally by using identical brick and mortar used in construction. An accurate material model is developed for masonry and employed in a computer program for the non-linear dynamic analysis of masonry buildings. The analytical results based on measured material properties indicated that masonry buildings which satisfy basic seismic code requirements possess remarkable lateral strength, stiffness and energy dissipation capacity. Accordingly, a simple elastic design approach is rendered suitable for unreinforced masonry under seismic excitations, provided that realistic material properties are employed in design.     

Numerical validation of analytical solutions and their use for equivalent-linear seismic analysis of circular tunnels

The first part of this paper presents an extensive validation of four analytical solutions for the seismic design of circular tunnels. The validation is performed with a quasi-static finite element (FE) model which conforms to the assumptions of the analytical solutions. Analyses are performed for a wide range of flexibility ratios, slippage conditions at soil–lining interface, assuming both drained and undrained behaviour. Based on the numerical predictions the relative merits of the considered analytical solutions are discussed and recommendations are given for their use in design. The second part of this paper explores the use of equivalent linear soil properties in analytical solutions as an approximate way of simulating nonlinearity. The results of equivalent linear site response analyses are used as an input for the analytical solutions. The comparison of the analytical predictions with nonlinear numerical analysis results is very satisfactory. The results of this study suggest that analytical solutions can be used for preliminary design using equivalent linear properties and the corresponding compatible strain as an approximate way of accounting for nonlinear soil response.     

Correlation studies on an RC frame shaking-table specimen

This paper presents the correlation of the results of a new model for the dynamic analysis of reinforced concrete (RC) frames with the experimental time history of a two storey RC frame shaking-table specimen. The frame member model consists of separate subelements that describe the deformations due to flexure, shear and bond slip in RC structural elements. The subelements are combined by superposition of flexibility matrices to form the frame element. A non-linear solution method which accounts for the unbalance of internal forces between different subelements during a given load increment is used with the model. The ability of the proposed model to describe the dynamic response of frame structures under earthquake excitations is evaluated by comparing the analytical results with experimental evidence from a two-storey, one bay reinforced concrete frame tested on the shaking-table. The model parameters for the shaking-table specimen are derived from available experimental evidence and first principles of reinforced concrete. The effect of reinforcing bar slip on the local and global dynamic response of the test structure is assessed. © 1997 John Wiley & Sons, Ltd.     

砌体结构抗震抗剪强度分析

进行了墙体抗剪强度理论和公式的研究。将主拉强度理论与剪摩强理论相结合,形成了一种新和强度理论,即拉摩强度理论。根据该理论,导出了墙体抗剪强度公式。给出了公式系数的确定方法,并确定了砖墙体的公式系数。将本文建议的砖墙体抗剪强度公式与抗震和砌体规范采用的抗剪强度公式进行了比较,比较结果表明：抗震规范公式值较小;砌体规范公式值较在,本文公式值介于两者中间。     

Effects of infill walls and floor diaphragms on the dynamic characteristics of a narrow‐rectangle building

Most buildings in Singapore are lightly reinforced concrete structures, which are mainly designed for gravity loading only, because Singapore is an island country located in a low‐to‐moderate seismic region. The dynamic properties of a typical high‐rise residential building with a long, narrow rectangular floor plan are studied using both experimental and numerical methods. The effects of the brick infill walls and the flexible diaphragms on the dynamic characteristics of the building are discussed in detail. The results from the ambient vibration tests are correlated with the numerical results of three different finite element models with different levels of sophistication. They include a bare frame model, a frame model with brick infill walls, and a frame model with both brick infill walls and flexible diaphragms. The dynamic properties of the third model match very well with the measured results in terms of both the natural frequencies and the mode shapes. The correlation results demonstrate the respective effects of the brick infill walls and the flexible diaphragms on the dynamic characteristics of the narrow‐rectangle building structure. Copyright © 2006 John Wiley & Sons, Ltd.     

Earthquake response of a multiblock nuclear reactor graphite core: Experimental model vs simulations

The complex dynamics of a quarter‐scale model of a graphite nuclear reactor core, representative of the second generation of British advanced gas‐cooled nuclear reactors, is investigated numerically and experimentally. Advanced gas‐cooled nuclear reactor cores are polygonal, multilayer, arrays of graphite bricks, with each brick allowed to rock by design relative to each other in accordance with the boundary conditions. A 35 000 DOF, nonlinear finite element model of the core created by Atkins Nuclear, was analysed on a high performance computing facility at the University of Bristol, and a corresponding 8 t physical model, equipped with 3200 data acquisition channels, was built and tested on the University of Bristol 6‐DOF shaking table. In this paper, the two models are subjected to a series of (1) synthetic earthquake and (2) idealised harmonic input motions. The experimental data are used to compare and verify the two models and explore the dynamics of the core. A kinematic model of the response is also developed based solely on geometric constraints. The results are presented in the form of response maps and graphs. Important conclusions are drawn as to the dynamics and earthquake response of such systems, which inform numerical model validation. It is found that contrary to the case of a small number of rocking blocks that exhibit highly complex response patterns, the behaviour of the model at hand is both smooth and repeatable. An analogy between the response of the core and that of dense granular matter exhibiting particle interlocking and dilatancy is highlighted.     

Parametric analysis of single pile response in laterally spreading ground

Extensive damage to pile-supported structures has been witnessed in several recent earthquakes (Chi-Chi, 1999; Kobe, 1995, etc.), as a result of liquefaction-induced lateral spreading of slightly sloping ground or free-face topographic irregularities. This paper presents a parametric analysis of the basic pile and soil parameters, as well as the pile-soil interaction mechanisms affecting the response of single piles subjected to such lateral spreading, based on numerical simulation with the nonlinear P-y method. In parallel, a set of design charts and analytical relations is established, for approximate computation of maximum pile deflections and bending moments, using a “theory guided” multi-variable statistical analysis of the numerical predictions. Three different combinations (design cases) of pile head constraints and soil conditions were considered, which are commonly encountered in practice. The overall accuracy of the proposed analytical relations is evaluated against experimental results from seven centrifuge and five large shaking table experiments.     

Overstrength of dowelled CLT connections under monotonic and cyclic loading

This paper presents an evaluation of overstrength based on an experimental study on dowelled connections in Cross Laminated Timber (CLT). Connection overstrength needs to be well understood in order to ensure that ductile system behaviour and energy dissipation can be achieved under seismic loading. Overstrength is defined as the difference between the code-based strength, using characteristic material strengths, and the 95th percentile of the true strength distribution. Many aspects contribute to total connection overstrength, which makes its definition challenging. In this study, half-hole embedment tests were performed on CLT to establish embedment strength properties and three point bending tests were performed to determine the fastener yield moment. Different connection layouts, making use of mild steel dowels and an internal steel plate, were tested under monotonic and cyclic loading to evaluate theoretically determined overstrength values and study the influence of cyclic loading on overstrength. Experimental results were compared with strength predictions from code provisions and analytical models for ductile response under monotonic loading. It was found that cyclic loading does not significantly influence overstrength for connections that respond in a mixed-mode ductile way indicating that in future more expedient monotonic test campaigns could be used. This work also provides further experimental data and theoretical considerations necessary for the estimation of a generally applicable overstrength factor for dowelled CLT connections.     

Aseismic design implications of near-fault san fernando earthquake records

Near-fault records of the 1971 San Fernando earthquake contain severe, long duration acceleration pulses which result in unusually large ground velocity increments. A review of these records along with the results of available theoretical studies of near-fault ground motions indicates that such acceleration pulses may be characteristic of near-fault sites in general. The results of an analytical study of a building severely damaged during the San Fernando earthquake indicate that such severe, long duration acceleration pulses were the cause of the main features of the observed structural damage. The implications of such pulses on current aseismic design methods, particularly those used to establish design earthquakes, are examined for buildings located near potential earthquake faults. Analytical studies of the non-linear dynamic response of single and multiple degree-of-freedom systems to several near-fault records, as well as to a more standard accelerogram, indicate that at near-fault sites: (a) very large displacement ductilities may result for current levels of code design forces; (b) smoothed elastic design response spectra should reflect the larger ground velocities that may occur; and (c) peak inelastic response cannot reliably be inferred from elastic response predictions.     

北京地区农村砖木结构振动台试验研究

为了了解北京地区典型砖木结构(木柱支撑,木屋盖,外砖墙)农村住宅结构的抗震能力,根据北京地区这类农村住宅结构的调研结果,本文介绍了一座典型砖木结构单层三开间农村住宅2/3缩尺振动台试验结构模型的设计与动力试验结果。按照北京地区8度抗震设防的要求,分别完成了模型在设计小震(0.072g)、中震(0.2g)和大震(0.4g)条件下的振动台动力试验,量测了模型的动力响应,记录了不同激励水平下模型的开裂情况。基于试验结果,分析了这种结构的抗震能力以及该类型房屋的抗震薄弱点,为制定这类结构的抗震加固方案提供依据。     

R/C frame–infill interaction model and its application to Indonesian buildings

This paper proposes a new analytical model for masonry‐infilled R/C frames to evaluate the seismic performance considering R/C frame–infill interactions. The proposed analytical model replaces masonry infill with a diagonal compression strut, which represents distributed compression transferred between frame and infill interfaces. The equivalent strut width is presented as a function of the frame–infill contact length, which can be evaluated by static equilibriums related to compression balance and lateral displacement compatibility at the frame–infill interfaces. The proposed analytical model was verified through comparisons with experimental results obtained for several brick masonry‐infilled R/C frames representing a typical R/C building with nonstructural masonry infill in Indonesia. As a result, good agreements were observed between the experimental and analytical values of the lateral strength and ductility of the infilled frames. The seismic performances of two earthquake‐damaged R/C buildings with different damage conditions were evaluated considering infill effects by applying the proposed analytical model. Consequently, the nonstructural brick masonry infill significantly affected the seismic resistances of the buildings, which seemed to lead to differing levels of damage for each building. These results indicate that the proposed analytical model can be an effective tool for more precisely screening earthquake‐vulnerable existing R/C buildings in Indonesia. Copyright © 2016 The Authors. Earthquake Engineering & Structural Dynamics Published by John Wiley & Sons Ltd.     

In‐plane and out‐of‐plane behavior of confined masonry walls for various toothing and openings details and prediction of their strength and stiffness

Eight half‐scale brick masonry walls were tested to study two important aspects of confined masonry (CM) walls related to its seismic behavior under in‐plane and out‐of‐plane loads. Four solid wall specimens tested to investigate the role of type of interface between the masonry and tie‐columns, such as toothing varying from none to every course. The other four specimens with openings were tested to study the effectiveness of various strengthening options around opening to mitigate their negative influence. In the set of four walls, one wall was infilled frame while the other three were CM walls of different configurations. The experimental results were further used to determine the accuracy of various existing models in predicting the in‐plane response quantities of CM walls. Confined masonry walls maintained structural integrity even when severely damaged and performed much better than infill frames. No significant effect of toothing details was noticed although toothing at every brick course was preferred for better post‐peak response. For perforated walls, provision of vertical elements along with continuous horizontal bands around openings was more effective in improving the overall response. Several empirical and semi‐empirical equations are available to estimate the lateral strength and stiffness of CM walls, but those including the contribution of longitudinal reinforcement in tie‐columns provided better predictions. The available equations along with reduction factors proposed for infills could not provide good estimates of strength and stiffness for perforated CM walls. However, recently proposed relations correlating strength/stiffness with the degree of confinement provided reasonable predictions for all wall specimens. Copyright © 2016 John Wiley & Sons, Ltd.     

Correlation studies using the equivalent base horizontal acceleration method

The equivalent base horizontal acceleration concept was developed for calculating the response of test structures to shaking table excitations, to account for pitching interaction effects of the table. Using the procedure, analysis-experiment comparisons were made of the shaking table tests of a 0–3-scale model of a six-storey concentrically K-braced steel structure. The correlation of the analytical and experimental results was excellent in both the elastic and inelastic ranges of structural response.     

多重孔岩石微分等效介质模型及其干燥情形下的解析近似式

经典的微分等效介质(DEM)理论可用于确定多孔介质的弹性性质,但由于缺乏多重孔DEM方程,其估计的多重孔岩石的等效弹性模量依赖于包裹体(即不同孔隙纵横比的孔或缝)的添加顺序.本文首先从Kuster-Toksöz理论出发建立了Zimmermann和Norris两种形式的多重孔DEM方程.Norris形式的多重孔DEM方程预测的等效弹性模量总是位于Hashin-Shtrikman上下限内,而Zimmermann形式的多重孔DEM方程有时会越界.然后,通过使用干燥岩石模量比的解析近似式,对两个相互耦合的Norris形式DEM方程进行解耦得到干燥多重孔岩石的体积和剪切模量解析式.用全DEM方程的数值解对解析近似式的有效性进行了测试,解析公式的计算结果在整个孔隙度分布区间与数值解吻合良好.对实验室测量数据在假设岩石含有双重孔隙的情形下用双重孔DEM解析公式对岩石的弹性模量进行了预测,结果表明,解析式准确地预测了弹性模量随孔隙度的变化.双重孔(即软、硬孔)DEM解析模型可用来反演各孔隙类型的孔隙体积比,它可以通过实验室测量与理论预测之间的平方误差最小反演得到.砂岩样品的反演结果揭示,软孔的孔隙体积百分比与粘土含量没有明显的相关性.     

Elastic moduli of dry rocks containing spheroidal pores based on differential effective medium theory

Differential effective medium (DEM) theory is applied to determine the elastic properties of dry rock with spheroidal pores. These pores are assumed to be randomly oriented. The ordinary differential equations for bulk and shear moduli are coupled and it is more difficult to obtain accurate analytical formulae about the moduli of dry porous rock. In this paper, we derive analytical solutions of the bulk and shear moduli for dry rock from the differential equations by applying an analytical approximation for dry-rock modulus ratio, in order to decouple these equations. Then, the validity of this analytical approximation is tested by integrating the full DEM equation numerically. The analytical formulae give good estimates of the numerical results over the whole porosity range. These analytical formulae can be further simplified under the assumption of small porosity. The simplified formulae for spherical pores (i.e., the pore aspect ratio is equal to 1) are the same as Mackenzie's equations. The analytical formulae are relatively easy to analyze the relationship between the elastic moduli and porosity or pore shapes, and can be used to invert some rock parameters such as porosity or pore aspect ratio. The predictions of the analytical formula for the sandstone experimental data show that the analytical formulae can accurately predict the variations of elastic moduli with porosity for dry sandstones. The effective elastic moduli of these sandstones can be reasonably well characterized by spheroidal pores, whose pore aspect ratio was determined by minimizing the error between theoretical predictions and experimental measurements. For sandstones the pore aspect ratio increases as porosity increases if the porosity is less than 0.15, whereas the pore aspect ratio remains relatively stable (about 0.14) if the porosity is more than 0.15.