CONFIGURATION OF A MULTISTOREY BUILDING SUBJECTED TO LATERAL FORCES
ASHRAF M.*,SEDIGHI Z.A.,JAVED M.A.

* DEPARTMENT OF CIVIL ENGINEERING, UNIVERSITY OF ENGINEERING AND TECHNOLOGY, LAHORE, PAKISTAN


A study has been carried out to determine the optimum configuration of a multistory building by changing shear walls location. Four different cases of shear wall position for a 25 storey building have been analyzed as a space frame system using a standard package ETAB subjected to lateral and gravity loading in accordance with UBC provisions.
It is found that columns and beams forces are found to increase on grids opposite to the changing position of shear wall away from the centroid of the building. Twisting moments in members are observed to be having increasing trend with enhancement in the eccentricity between geometrical centroid of the building and shear wall position. Stresses in shear wall elements have more pronounced effect in elements parallel to displaced direction of shear wall as compared to those in perpendicular direction.
The lateral displacements of the building are uniform for a zero eccentricity case. On the contrary, the drift is more on grids on one side than that of the others in case of eccentric shear wall position. It is concluded that the shear wall should be placed at a point by coinciding center of gravity and centroid of the building.


Keyword: SHEAR WALL, LATERAL LOADING, ECCENTRICITY, DRIFT, FORCES, STRESSES
ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING AND HOUSING) 2008; 9(5):525-537.

http://sid.ir/en/VEWSSID/J_pdf/103820080503.pdf

WAVELET ANALYSIS FOR PROCESSING OF EARTHQUAKE RECORDS

HEYDARI A.*,SALAJEGHEH E.

* UNIVERSITY OF SHAHREKORD, SHAHREKORD, IRAN


Wavelet analysis is a new mathematical technique and in the recent years enormous interest in application of engineering has been observed. This new technique is particularly suitable for non-stationary processes as in contrast to the Fourier transform. The wavelet transform allows exceptional localization, both in time and frequency domains. The application of the wavelet transform to earthquake engineering is rare. In this paper the wavelet transform capability to give a full time–frequency representation of the earthquake record is demonstrated. In this method, the time series of the earthquake record, breaking at the tropical coral reefs and mechanically generated waves in the wave flume demonstrates the ability of the wavelet transform technique to detect a complex variability of these signals in the time–frequency domain. Various spectral representations resulting from the wavelet transform are discussed and their application for earthquake record is shown.


Keyword: TIME HISTORY, FREQUENCY LOCALIZATION, WAVELET TRANSFORM, FOURIER TRANSFORM


ASIAN JOURNAL OF CIVIL ENGINEERING (BUILDING AND HOUSING) 2008; 9(5):513-524.

http://sid.ir/en/VEWSSID/J_pdf/103820080505.pdf

منبع: http://mahdihashemi.blogfa.com/post-620.aspx
Base Isolation for Earthquake Resistance
It is easiest to see the principle at work by referring directly to the most widely used of these advanced techniques, known as base isolation. A base isolated structure is supported by a series of bearing pads, which are placed between the buildings and building foundation.


The concept of base isolation is explained through an example building resting on frictionless rollers. When the ground shakes, the rollers freely roll, but the building above does not move. Thus, no force is transferred to the building due to the shaking of the ground; simply, the building does not experience the earthquake. Now, if the same building is rested on the flexible pads that offer resistance against lateral movements, then some effect of the ground shaking will be transferred to the building above. If the flexible pads are properly chosen, the forces induced by ground shaking can be a few times smaller than that experienced by the building built directly on ground, namely a fixed base building. The flexible pads are called base-isolators, whereas the structures protected by means of these devices are called base-isolated buildings. The main feature of the base isolation technology is that it introduces flexibility in the structure.



Traditional Earthquake Mitigation Techniques


Base Isolation Technique


Due to the flexibility in the structure, a robust medium-rise masonry or reinforced concrete building becomes extremely flexible. The isolators are often designed, to absorb energy and thus add damping to the system. This helps in further reducing the seismic response of the building. Many of the base isolators look like large rubber pads, although there are other types that are based on sliding of one part of the building relative to other. Also, base isolation is not suitable for all buildings. Mostly low to medium rise buildings rested on hard soil underneath; high-rise buildings or buildings rested on soft soil are not suitable for base isolation.

Lead-rubber bearings are the frequently-used types of base isolation bearings. A lead rubber bearing is made from layers of rubber sandwiched together with layers of steel. In the middle mahdihashemi.blogfa.com the solid lead "plug". On top and bottom, the bearing is fitted with steel plates which are used to attach the bearing to the building and foundation. The bearing is very stiff and strong in the vertical direction, but flexible in the horizontal direction.



Working Principle
To get a basic idea of how base isolation works, first examine the `(fig b). This shows an earthquake acting on base isolated building and a conventional, fixed-base, building. As a result of an earthquake, the ground beneath each building begins to move. In (fig b) it is shown moving to left. Each building responds with movement which tends towards the right. The buildings displacement in the direction opposite the ground motion is actually due to inertia. The inertia forces acting on a building are the most important of all those generated during an earthquake.

In addition to displacing towards right, the un-isolated building is also shown to be changing its shape from a rectangle to a parallelogram. We say that the building is deforming. The primary cause of earthquake damage to buildings is the deformation which the building undergoes as a result of the inertial forces upon it.mahdihashemi.blogfa.com/



RESPONSE OF BASE ISOLATED BUILDINGS
The base-isolated building retains its original, rectangular shape. The base isolated building itself escapes the deformation and damage-which implies that the inertial forces acting on the base isolated building have been reduced. Experiments and observations of base-isolated buildings in earthquakes to as little as ¼ of the acceleration of comparable fixed-base buildings.

Acceleration is decreased because the base isolation system lengthens a buildings period of vibration, the time it takes for a building to rock back and forth and then back again. And in general, structures with longer periods of vibration tend to reduce acceleration, while those with shorter periods tend to increase or amplify acceleration.



SECOND TYPE OF BASE ISOLATION


Spherical sliding isolation systems are another type of base isolation. The building is supported by bearing pads that have a curved surface and low friction. During an earthquake the building is free to slide on the bearings. Since the bearings have a curved surface, the building slides both horizontally and vertically. The forces needed to move the building upwards limits the horizontal or lateral forces which would otherwise cause building deformations. Also by adjusting the radius of the bearings curved surface, this property can be used to design bearings that also lengthen the buildings period of vibration.

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