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Abstract
In this study, the response and behavior of machine foundations resting on dry and saturated sand was investigated experimentally. A physical model was manufactured to simulate steady state harmonic load applied on a footing resting on sandy soil at different operating frequencies. Total of (84) physical models were performed. The parameters that were taken into consideration include loading frequency, size of footing and different soil conditions. The footing parameters are related to the size of the rectangular footing and depth of embedment. Two sizes of rectangular steel model footing were used. The footings were tested by changing all parameters at the surface and at 50 mm depth below model surface. Meanwhile, the investigated parameters of the soil condition include dry and saturated sand for two relative densities; 30 % and 80 %. The dynamic loading was applied at different operating frequencies. The response of the footing was elaborated by measuring the amplitude of displacement using the vibration meter. The response of the soil to dynamic loading includes measuring the stresses inside soil media by using piezoelectric sensors. It was concluded that the final settlement (St) of the foundation increases with increasing the amplitude of dynamic force, operating frequency and degree of saturation. Meanwhile, it decreases with increasing the relative density of sand, modulus of elasticity and embedding inside soils. The maximum displacement amplitude exhibits its maximum value at the resonance frequency, which is found to be about 33.34 to 41.67 Hz. In general, embedment of footing in sandy soils leads to a beneficial reduction in dynamic response (displacement and excess pore water pressure) for all soil types in different percentages accompanied by an increase in soil strength.

Key Words
dynamic; saturated soil; machine foundation; displacement

Address
Mohammed Y. Fattah: Building and Construction Engineering Department, University of Technology, Baghdad, Iraq Mosa J. Al-Mosawi and Abbas F.I. Al-Ameri: College of Engineering University of Baghdad, Iraq

Abstract
This paper examines the contribution of three sources of uncertainties to probabilistic seismic behaviour of wood frame buildings, including ground motions, intensity and seismic mass. This sensitivity analysis is performed using three methods, including the traditional method based on the conditional distributions of ground motions at given intensity measures, a method using the summation of conditional distributions at given ground motion records, and the Monte Carlo simulation. FEMA P-695 ground motions and its scaling methods are used in the analysis. Two archetype buildings are used in the sensitivity analysis, including a two-storey building and a four-storey building. The results of these analyses indicate that using data-fitting techniques to obtain probability distributions may cause some errors. Linear interpolation combined with data-fitting technique may be employed to improve the accuracy of the calculated exceeding probability. The procedures can be used to quantify the risk of wood frame buildings in seismic events and to calibrate seismic design provisions towards design code improvement.

Key Words
earthquake engineering; probability; reliability; wood frame structures; timber; seismic effect

Address
Jianzhong Gu: Architectural and Engineering Technology, Thompson Rivers University, 900 McGill Rd, Kamloops, BC, Canada

Abstract
This paper presents He´s Energy Balance Method (EBM) for solving nonlinear oscillatory differential equations. Three strong nonlinear cases have been studied analytically. Analytical results of the EBM are compared with numerical solutions using Runge-Kutta´s algorithm. The effects of different important parameters on the nonlinear response of the systems are studied. The results show the presented method is potentially to solve high nonlinear vibration equations.

Key Words
Energy Balance Method (EBM); Runge- Kutta´s Method (RKM); nonlinear vibrations

Address
Mahmoud Bayat: Young Researchers and Elite Club, Roudehen Branch, Islamic Azad University, Roudehen, Iran Iman Pakar and Mahdi Bayat: Young Researchers and Elite club, Mashhad Branch, Islamic Azad University, Mashhad, Iran

Abstract
Fiber models have been developed and applied to various structural elements such as shear walls, beams and columns. Only scarcely have fiber models been applied to circular foundation systems such as cast in drilled holes shafts (CIDH). In pile foundations with constraint head boundary conditions, shear deformations can easily contribute to the lateral pile response. However, soil structure interaction formulations such as the p-y method, commonly used for lateral pile design, do not include structural shear deformations in its traditional derivation method. A fiber model that couples shear and axial-bending behavior, originally developed for wall elements was modified and validated on circular cross sections (columns) before being applied to a 0.61 m diameter reinforced concrete (RC) pile with fixed head boundary conditions. The analytical response was compared to measured test results of a fixed head test pile to investigate the possible impact of pile shear deformations on the displacement, shear, and moment profiles of the pile. Results showed that shear displacements and forces are not negligible and suggest that nonlinear shear deformations for RC piles should be considered for fixed-head or similar conditions. Appropriate sensor layout is recommended to capture shear deformation when deriving p-y curves from field measurements.

Key Words
piles; lateral loading; soil-pile interaction; shear deformations; reinforced concrete

Address
Anne Lemnitzer: Department of Civil Engineering, Univ. of California Irvine, 4135 Eng. Gateway, Irvine, CA, 92697, USA Eduardo Nunez: Independent Structural Engineer, Santiago, Chile Leonardo M. Massone: Department of Civil Engineering, University of Chile, Santiago, Blanco Encalada 2002, Santiago, Chile

Abstract
The effectiveness of 100/30, 100/40 and SRSS directional combination rules on the response of asymmetric setback buildings is examined. Because of the irregularity in setback buildings, the maximum seismic response would be correlative with the direction of earthquake. To verify the directional combination rules of mode superposition methods, the time history analyses of setback buildings to real earthquake records are carried out. Example analyses have been used to compare the validty and accuracy of SRSS and percentage methods for frame and dual frame-wall systems.

Key Words
combination rules; seismic analysis; multi-story buildings; asymmetric set-backs

Address
M. Gunhan Aksoylu, Yavuz Durguna and Kutlu Darilmaz: Istanbul Technical University, Civil Engineering Department, Maslak, Sariyer, 34469, Istanbul, Turkey

Abstract
The goal of energy-based seismic design is to obtain a structural design with a higher energy dissipation capacity than the energy dissipation demands incurred under earthquake motions. Accurate estimation of the story hysteretic energy demand of a multi-story structure is the key to meeting this goal. Based on the assumption of a mode-equivalent single-degree-of-freedom system, the energy equilibrium relationship of a multi-story structure under seismic action is transformed into that of a multi-mode analysis of several single degree-of-freedom systems. A simplified equation for the estimation of the story seismic hysteretic energy demand was then derived according to the story shear force and deformation of multi-story buildings, and the deformation and energy relationships between the mode-equivalent single-degree-offreedom system and the original structure. Sites were categorized into three types based on soil hardness, namely, hard soil, intermediate hard (soft) soil, and soft soil. For each site type, a 5-story and 10-story reinforced concrete frame structure were designed and employed as calculation examples. Fifty-six earthquake acceleration records were used as horizontal excitations to validate the accuracy of the proposed method. The results verify the following. (1) The distribution of seismic hysteretic energy along the stories demonstrate a degree of regularity. (2) For the low rise buildings, use of only the first mode shape provides reasonably accurate results, whereas, for the medium or high rise buildings, several mode shapes should be included and superposed to achieve high precision. (3) The estimated hysteretic energy distribution of bottom stories tends to be underestimated, which should be modified in actual applications.

Key Words
hysteretic energy demand; nonlinear response history analysis; pushover analysis; equivalent SDOF system; earthquake excitation

Address
Feng Wang, Zhiyu Huang: College of Civil Engineering, Dalian Minzu University, Dalian, China Ning Zhang: Dalian Polytechnic University, Dalian, China

Abstract
Rehabilitation of historical unreinforced masonry (URM) buildings is a priority in many parts of the world, since those buildings are a living part of history and a testament of human achievement of the era of their construction. Many of these buildings are still operational; comprising brittle materials with no reinforcements, with spatially distributed mass and stiffness, they are not encompassed by current seismic assessment procedures that have been developed for other structural types. To facilitate the difficult task of selecting a proper rehabilitation strategy - often restricted by international treaties for non-invasiveness and reversibility of the intervention - and given the practical requirements for the buildings´ intended reuse, this paper presents a practical procedure for assessment of seismic demands of URM buildings - mainly historical constructions that lack a well-defined diaphragm action. A key ingredient of the method is approximation of the spatial shape of lateral translation, Φ, that the building assumes when subjected to a uniform field of lateral acceleration. Using Φ as a 3-D shape function, the dynamic response of the system is evaluated, using the concepts of SDOF approximation of continuous systems. This enables determination of the envelope of the developed deformations and the tendency for deformation and damage localization throughout the examined building for a given design earthquake scenario. Deformation demands are specified in terms of relative drift ratios referring to the in-plane and the out-of-plane seismic response of the building´s structural elements. Drift ratio demands are compared with drift capacities associated with predefined performance limits. The accuracy of the introduced procedure is evaluated through (a) comparison of the response profiles with those obtained from detailed time-history dynamic analysis using a suite of ten strong ground motion records, five of which with near-field characteristics, and (b) evaluation of the performance assessment results with observations reported in reconnaissance reports of the field performance of two neoclassical torsionally-sensitive historical buildings, located in Thessaloniki, Greece, which survived a major earthquake in the past.

Key Words
seismic assessment; historical and monumental buildings; unreinforced masonry structures (URM); pushover analysis; torsion

Address
tylianos I. Pardalopoulos, Stavroula J. Pantazopoulou: Department of Civil and Environmental Engineering, University of Cyprus, Nicosia, Cyprus Stylianos I. Pardalopoulos: Institute of Engineering Seismology and Earthquake Engineering, Thessaloniki, Greece Stavroula J. Pantazopoulou: Department of Civil Engineering, Lassonde Faculty of Engineering, York University, Canada Christos E. Ignatakis: Department of Civil Engineering, Aristotle University of Thessaloniki, Thessaloniki, Greece

Abstract
The linear and nonlinear seismic responses of steel buildings with perimeter moment resisting frames and welded connections (WC) are estimated and compared with those of buildings with posttensioned connections (PC). Two-dimensional (2D) and three-dimensional (3D) structural representations of the buildings as well as global and local response parameters are considered. The seismic responses and structural damage of steel buildings with PC may be significantly smaller than those of the buildings with typical WC. The reasons for this are that the PC buildings dissipate more hysteretic energy and attract smaller inertia forces. The response reduction is larger for global than for local response parameters. The reduction may significantly vary from one structural representation to another. One of the main reasons for this is that the energy dissipation characteristics are quite different for the 2D and 3D models. In addition, in the case of the 3D models, the contribution of each horizontal component to the axial load on an specific column may be in phase each other during some intervals of time, but for some others they may be out of phase. It is not possible to observe this effect on the 2D structural formulation. The implication of this is that 3D structural representation should be used while estimating the effect of the PC on the structural response. Thus, steel frames with post-tensioned bolted connections are a viable option in high seismicity areas due to the fact that brittle failure is prevented and also because of their reduced response and self-centering capacity.

Key Words
steel buildings; welded and post-tensioned connections; nonlinear analysis; seismic loading; 2D and 3D structural representation

Address
Alfredo Reyes-Salazar, Eden Bojorquez, Juan Bojorquez and Mario D. Llanes-Tizoc: Facultad de Ingenieria, Universidad Autonoma de Sinaloa, Ciudad Universitaria, Culiacan Sinaloa, Mexico Sonia E. Ruiz: Instituto de Ingenieria, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico D.F., Mexico

Abstract
A suitable ground motion intensity measure (IM) plays a crucial role in the seismic performance assessment of a structure. In this paper, we introduce a scalar IM for use in evaluating the seismic response of single-layer reticulated domes. This IM is defined as the weighted geometric mean of the spectral acceleration ordinates at the periods of the dominant vibration modes of the structure considered, and the modal strain energy ratio of each dominant vibration mode is the corresponding weight. Its applicability and superiority to 11 other existing IMs are firstly investigated in terms of correlation with the nonlinear seismic response, efficiency and sufficiency using the results of incremental dynamic analyses which are performed for a typical single-layer reticulated dome. The hazard computability of this newly proposed IM is also briefly discussed and illustrated. A conclusion is drawn that this dominant vibration mode-based scalar IM has the characteristics of strong correlation, high efficiency, good sufficiency as well as hazard computability, and thereby is appropriate for use in the prediction of seismic response of single-layer reticulated domes.

Key Words
ground motion intensity measure; nonlinear seismic response; single-layer reticulated domes; incremental dynamic analysis; modal strain energy ratio

Address
Jie Zhong, Xudong Zhi and Feng Fan: Key Laboratory of Structures Dynamic Behavior and Control of the Ministry of Education, Harbin Institute of Technology, Harbin 150090, China Jie Zhong, Xudong Zhi and Feng Fan: School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China

Abstract
Environmental and operational benefits of green roofs are manifolds; however, their main disadvantages are cost and weight. New technology enabled the use of plastics to reduce the weight of green roof systems to promote their installation. To maximize their potential benefits, green roofs can be installed on existing structures. This study evaluates the influence of green roofs on the seismic response of 3, 6, and 8 storey reinforced concrete ductile moment resisting frames, which were designed according to current seismic standards, however, not designed for green roofs. For each frame, three different types of roofs are considered: gravel flat roof, extensive green roof, and intensive green roof. Nonlinear dynamic time history analysis using an ensemble of twenty real earthquake records was performed to determine the inter-storey drift demand and roof drift demand for each frame. Eigenvalue analysis was also performed to determine the impact of green roofs weight on the elastic and cracked periods of the structure. Results from the analysis demonstrated that intensive and extensive green roofs do not affect the seismic performance of reinforced concrete frame structures.

Key Words
green roofs; RC frames; dynamic time history analysis; seismic response; base shear; drift

Address
Fabricio Bianchini, A.B.M. Rafiqul Haque, Kasun Hewage and M. Shahria Alam: School of Engineering, University of British Columbia, Kelowna, Okanagan School of Engineering, EME 4225, 1137 Alumni Ave., Kelowna, BC, Canada

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