Techno Press
Tp_Editing System.E (TES.E)
Login Search


eas
 
CONTENTS
Volume 9, Number 2, August 2015
 

Abstract
The effects of infill panels on the response of r.c. frames subjected to seismic action are widely recognized. Numerous experimental investigations were effected and several analytical models were developed on this subject. This work, which is part of a larger project dealing with specific materials and structures commonly used in Italy, discusses experimental tests on masonry and samples of bare and infilled portals. The experimental activity includes tests on elemental materials, and 12 wall samples. Finally, three one-bay one-story reinforced concrete frames, designed according to the outdated Italian technical code D.M. 1996 without seismic details, were tested (bare and infilled) under constant vertical and cyclic lateral load. The first cracks observed on the framed walls occurred at a drift of about 0.3%, reaching its maximum capacity at a drift of 0.5% while retaining its capacity up to a drift of 0.6%. Infill contributed to both the stiffness and strength of the bare reinforced concrete frame at small drifts thus improving overall system behavior. In addition to the experimental activities, previously mentioned, the recalibration of a model proposed by Comberscue (1996) was evaluated. The accuracy of an OpenSees non linear fiber based model of the prototype tested, including a strut element was verified through a comparison with the final experimental results. This work has been partially supported by research grant DPC-ReLUIS 2014.

Key Words
seismic response; infilled frames; masonry; cyclic test

Address
Alessandro Vittorio Bergami and Camillo Nuti: University of Roma Tre, Department of Architecture, Largo G. B. Marzi 10, Rome, Italy

Abstract
The present paper is devoted to study SH-wave propagation in heterogeneous layer laying over an inhomogeneous isotropic elastic half-space. The dispersion relation for propagation of said waves is derived with Green#39;s function method and Fourier transform. As a special case when the upper layer and lower half-space are homogeneous, our derived equation is in agreement with the general equation of Love wave. Numerically, it is observed that the velocity of SH-wave increases with the increase of inhomogeneity parameter.

Key Words
non-homogeneity; Fourier transformation; Green's function; Dirac-delta function; isotropic; SH-waves

Address
Rajneesh Kakar: Faculty of Engineering & Technology, GNA University, Phagwara-144405, India

Abstract
Existing building structures can easily present material mechanical properties which can largely vary even within a single structure. The current European Technical Code, Eurocode 8, does not provide specific instructions to account for high variability in mechanical properties. As a consequence of the high strength variability, at the occurrence of seismic events, the structure may evidence unexpected phenomena, like torsional effects, with larger experienced deformations and, in turn, with reduced seismic performance. This work is focused on the reduction in seismic performance due to the concrete strength variability. The analysis has been performed on a case-study, i.e., a 3D RC framed 4 storey building. A Normal distribution, compatible to a large available database, has been taken to represent the concrete strength domain. Different plan layouts, representative of realistic strength distributions, have been considered, and a statistical analysis has been performed on the induced reduction in seismic performance. The obtained results have been compared to the standard analysis as provided by Eurocode 8 for existing buildings. The comparison has shown that the Eurocode 8 provisions are not conservative for existing buildings having a large variability in concrete strength.

Key Words
RC framed structures; plan irregularity; torsional effects; concrete mechanical properties; RC existing buildings; seismic performance

Address
Department of Architecture (DiDA), University of Florence Piazza Brunelleschi, 6-50121 Firenze, Italy

Abstract
Ancient masonry towers constitute a relevant part of the cultural heritage of humanity. Their earthquake protection is a topic of great concern among researchers due to the strong damage suffered by these brittle and massive structures through the history. The identification of the seismic behavior and failure of towers under seismic loading is complex. This strongly depends on many factors such as soil characteristics, geometry, mechanical properties of masonry and heavy mass, as well as the earthquake frequency content. A deep understanding of these aspects is the key for the correct seismic vulnerability evaluation of towers and to design the most suitable retrofitting measure. Recent tendencies on the seismic retrofitting of historical structures by means of prestressing are related to the use of smart materials. The most famous cases of application of prestressing in towers were discussed. Compared to horizontal prestressing, vertical post-tensioning is aimed at improving the seismic behavior of towers by reducing damage with the application of an overall distribution of compressive stresses at key locations.

Key Words
towers; old masonry; earthquakes; vulnerability; behavior; failure modes; retrofitting

Address
Adolfo Preciado: Department of Civil Engineering, Polytechnical University of Guadalajara (UPZMG) Carretera Tlajomulco Santa Fe 595, 45640 Tlajomulco, Jalisco, Mexico

Gianni Bartoli: Department of Civil Engineering, University of Florence Via di Santa Marta 3, 50139 Florence, Italy

Harald Budelmann: Department of Civil Engineering, Technical University of Braunschweig Beethovenstrasse 52,
38106 Braunschweig, Germany

Abstract
In this paper, the effects of different types of irregularity along the height on the seismic responses of moment resisting frames are investigated using nonlinear dynamic analysis. Furthermore, the applicability of consecutive modal pushover (CMP) procedure for computing the seismic demands of vertically irregular frames is studied and the advantages and limitations of the procedure are elaborated. For this purpose, a special moment resisting steel frame of 10-storey height was selected as reference regular frame for which the effect of higher modes is important. Forty vertically irregular frames with stiffness, strength, combined-stiffness-and-strength and mass irregularities are created by applying two modification factors (MF=2 and 4) in four different locations along the height of the reference frame. Seismic demands of irregular frames are computed by using the nonlinear response history analysis (NL-RHA) and CMP procedure. Modal pushover analysis (MPA) method is also carried out for the sake of comparison. The effect of different types of irregularity along the height on the seismic demands of vertically irregular frames is investigated by studying the results obtained from the NL-RHA. To demonstrate the accuracy of the enhanced pushover analysis methods, the results derived from the CMP and MPA are compared with those obtained by benchmark solution, i.e., NL-RHA. The results show that the CMP and MPA methods can accurately compute the seismic demands of vertically irregular buildings. The methods may be, however, less accurate especially in estimating plastic hinge rotations for weak or weak-and-soft top and middle storeys of vertically irregular frames.

Key Words
vertically irregular frame; stiffness irregularity; strength irregularity; combined-stiffness-and-strength irregularity; mass irregularity; nonlinear response history analysis (NL-RHA); consecutive modal pushover analysis

Address
Moosa Ebrahimi Nezhad and Mehdi Poursha: Faculty of Civil Engineering, Sahand University of Technology, Tabriz, Iran

Abstract
Staircase is a vertical transportation element commonly used in every multistoried structure. Inclined flights of staircase are usually casted monolithically with RC frame. The structural configuration of stairs generally introduces discontinuities into the typical regular reinforced concrete frame composed of beams and columns. Inclined position of flight transfers both vertical as well as horizontal forces in the frame. Under lateral loading, staircase in a multistory RC frame building develops truss action creating a local stiffening effect. In case of seismic event the stiff area around staircase attracts larger force. Therefore, special attention is required while modeling and analyzing the building with staircase. However, in general design practice, designers usually ignore the staircase while modeling either due to ignorance or to avoid complexity. A numerical study has been conducted to examine the effect of ignoring staircase in modeling and design of RC frame buildings while they are really present in structure, may be at different locations. Linear dynamic analysis is performed on nine separate building models to evaluate influence of staircase on dynamic characteristics of building, followed by nonlinear static analysis on the same models to access their seismic performance. It is observed that effect of ignoring staircase in modeling is severe and leads to unsafe structure. Effect of location and orientation of staircase is also important in determining seismic performance of RC frame buildings.

Key Words
RC frame buildings; staircase; modeling; capacity curve; nonlinear static analysis

Address
Onkar G. Kumbhar, Ratnesh Kumar: Department of Applied Mechanics, Visvesvaraya National Institute of Technology,
Nagpur-440010, Maharashtra, India

Shrabony Adhikary: Department of Earthquake Engineering, Indian Institute of Technology, Roorkee-247667, Uttarakhand, India

Abstract
Damage of torsionally coupled buildings situated on soil sites has been reported in literature, however no site-specific studies are available for torsionally coupled buildings having site characteristics as a parameter. Effect of torsion is being accounted in seismic codes by the provision of design eccentricity where the dynamic to static eccentricity ratio is a parameter. In this paper, a methodology to determine dynamic to static eccentricity ratio of torsionally coupled buildings has been demonstrated for Delhi region for two torsionally coupled buildings on three soil sites. The variations of average and standard deviations of frame shears for stiff and flexible edges are studied for four eccentricity ratios for the two buildings for the three sites. From the limited studies made, it is observed that the dynamic to static eccentricity ratios observed for site-specific earthquakes are different from Indian seismic code specified value, hence a proposal is made to include a comment in Indian seismic code. Methodology proposed in this paper can be adopted for any region, for the estimation of dynamic to static eccentricity ratio for site specific earthquake.

Key Words
dynamic eccentricity; seismic code; site-specific earthquake; torsionally coupled building; Delhi

Address
P. Kamatchi, Nagesh R. Iyer: CSIR-Structural Engineering Research Centre, Chennai, India

G.V. Ramana, A.K. Nagpal: Indian Institute of Technology, Delhi, India

J.A. Bhat: National Institute of Technology, Srinagar, India

Abstract
Integral abutment bridges have many advantages over bridges with expansion joints in terms of economy and maintenance costs. However, in the design of abutments of integral bridges temperature loads play a crucial role. In addition, seismic loads are readily transferred to the substructure and affect the design of these components significantly. Currently, the European and American bridge design codes consider these two load cases separately in their recommended design load combinations. In this paper, the importance and necessity of combining the thermal and seismic loads is investigated for integral bridges. A 2D finite element combined pile-soil-structure interactive model is used in this evaluation. Nonlinear behavior is assumed for near field soil behind the abutments. The soil around the piles is modeled by nonlinear springs based on p-y curves. The uniform temperature changes occurring at the time of some significant earthquakes around the world are gathered and applied simultaneously with the corresponding earthquake time history ground motions. By comparing the results of these analyses to prescribed AASHTO LRFD load combinations it is observed that pile forces and abutment stresses are affected by this new load combination. This effect is more severe for contraction mode which is caused by negative uniform temperature changes.

Key Words
integral bridge; nonlinear model; seismic load; thermal load; soil-structure interaction

Address
Narges Easazadeh Far, Majid Barghian: Department of Civil Engineering, Tabriz University, Tabriz, Iran

Shervin Maleki: Department of Civil Engineering, Sharif University of Technology, Azadi Ave., Tehran, Iran

Abstract
A destructive earthquake, the magnitude of this earthquake was 7.2, hit Van, Turkey on October 23, 2011. After this devastating earthquake, a moderate earthquake which had 5.7 magnitude on November 9, 2011 occurred in Edremit, Van. These earthquakes caused heavy damages and collapses in many reinforced concrete buildings with loss of lives. In this paper, characteristics of ground motions of these earthquakes were studied and, deficiencies in structural elements and engineering faults such as poor workmanship and quality of construction, soft and weak stories, strong beam-weak column, short column, large overhang, hammering and unconfined gable wall were investigated. According to the observations, it was seen that, low quality of structural materials, lack of engineering services, inappropriate design and construction with insufficient detailing of the structural elements were the main reasons of heavy damages.

Key Words
2011 Van earthquakes; ground motion characteristics; reinforced concrete buildings; earthquake damages

Address
Burak Yon: Department of Civil Engineering, Dicle University, Diyarbakir, Turkey

Erkut Sayin, Yusuf Calayir, Zulfu cinar Ulucan, Mehmet Karatas, Humeyra Sahin, Kursat Esat Alyamac and Abdullah Tevfik Bildik: Department of Civil Engineering, Firat University, Elazig, Turkey


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2017 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: info@techno-press.com