Journal of Engineering Geology

Effects of Soil Type on the Rehabilitation Design of Masonry Buildings by Shotcrete Method Considering Seismic Classification

M.A Eskandari

Most of masonry buildings are vulnerable against earthquakes and need to be rehabilitated. One of the pragmatic methods for strengthening is to utilize shotcreting the masonry walls. In this paper the effects of the soil type (in view of seismic behavior) on the rehabilitation of the masonry building by shotcrete are investigated. Three types of masonry buildings are simulated by ABAQUS software and analyzed against three earthquake records to find their reporses and seismic demands. Using five types of shotcrete configuration consisted of shotcrete strips in vertical and horizontal directions for rehabilitation are studied to find the appropriate method for damage mitigation. The suitable method for rehabilitation are used to study the effects of soil type on the rehabilitated buildings. Three records of the Tabas (1979) earthquake which were recorded on different types of soils (Type I, II and III based on the Iranian seismic design regulations) are considered to analyze the sample masonry building. The results show that the shotcrete method is more effective for buildings which are relying on the softer soils and in stiff soils it is recommended to combine the shotcrete method with other rehabilitation methods which are able to strengthen the building without increasing the stiffness of the building, like utilizing post tensioning cables.

Seismic Performance of Steel Bundled Tube Structures under Scaled Near-Field Records according to the Iranian Seismic Code 2800 - 3rd & 4th Editions

Afshin Meshkat-Dini

This research is focused on an analytical approach to investigate the seismic performance of tall building under scaled near-field earthquake records. To achieve this objective, it is employs medium to high rise steel bundled-tube rigid frames. The examined structures are designed according to the Iranian seismic code 2800 (4th edition). To study the seismic response, groups of near field earthquake records with their associated properties are selected to perform non-linear time history analyses. The most important characteristic of the chosen near-field earthquake records is the presence of powerful long-term velocity pulses which distinguishes them from far-field earthquake records. The first part of the mentioned ensemble includes two recorded strong ground motions in Iran i.e. Tabas 1978 and Bam 2003, respectively and two powerful records of the Northridge 1994 earthquake. The second part contains one far-field record of the Northridge 1994 earthquake. The selected records are scaled based on the Iranian seismic code 2800 (3rd and 4th editions). The characteristics of seismic performance of each structural model, including maximum relative displacement of each story, seismic base shear and the formation of plastic hinges in the resistant skeleton have been carefully evaluated. The results indicate that using the 4th edition of the Iranian seismic code 2800 produces noticeably lower values of scale factor and their associated seismic responses in the studied structures as well as the nonlinear demand of the main load bearing members under scaled records with those factors, compared to the corresponding analytical cases based on the 3rd edition of the Iranian seismic code 2800. According to the results of this study, the rate of the drift parameter variations of structures that have been evaluated on the basis of seismic code 4th edition in comparison with the seismic code 2800 are experiencing a relative reduction about 30%.

An Experimental Investigation of Dynamic Force on the Walls of Buried Tanks using Shaking Table Testing in Comparison to Analytical Method Relations

H Hataminia

Tanks are structures for storing fluids that are made in different sizes, shapes and genera. Today using of tanks for water, petroleum products storage, and industrial wastes, has been developed significantly. The buried rectangular concrete tanks are used for water supply in most cities in our country. Soil-structure interaction is one of the most important issues in seismic behavior of buried tanks. With respects to code 123 that has suggested Mononobe-Okabe equation for dynamic pressure of earthquake excitation, the purpose of this research is to achieve the dynamic pressure of soil during earthquake. The obtained results have been compared to analytical and other experimental researches. Therefore, a series of small-scale experimental tests were conducted using 1g shaking table testing in the laboratory of physical modeling at University of Tehran. The results illustrate that dynamic force and pressure from Mononobe-Okabe and Wood equation are greater than experimental testing results. However Seed-Whitman equation is closer to experimental results.

Effect of Mainshock-Aftershock Sequence of Ground Motions on Inelastic Response of RC Frame

S.A Hosseini

In seismic prone areas, earthquakes happen more than just main shocks which are happen with sequences of shocks include of different intensity of aftershocks. In technical documents, these kinds of several earthquakes are called mainshock-aftershock ground motions. In this study, seismic behavior of RC frame under mainshock-aftershock with different ratios of maximum acceleration of aftershock to maximum acceleration of mainshock was evaluated. In this paper, nonlinear time-history analysis of frame were performed under mainshock-aftershock sequences and then the residual interstory drift ratio for comparing response of frame under seismic sequences was evaluated. The results show that, residual interstory drift ratio of frame, related to intensity of aftershocks to mainshock and enhance of intensity of aftershock due to increase residual interstory drift ratio of frame. Although, growth of residual interstory drift ratio of top stories more significant than below stories of frame.

Behavioral Properties of Hardness, Ultimate Capacity and Ductility of a new Semi-Rigid Connection

H H.Lavasani

With regard to the increase of computing power in the past decades, finite element methods have been used to obtain the graphs of rotational moment curves which reflect non-linear effect in connections response. Several common semi-rigid connections are modeled and their behavioral properties are briefly reviewed, then the details related to a new semi-fixed connection have been provided. The behavioral properties like hardness, ultimate capacity and ductility are investigated and compared to other simulated connections. To perform non-linear analyses of connection, finite element software ABAQUS is used. In this simulation, it has been tried to have inter-component interactions according to reality as much as possible. Bolted connections are modeled exactly and the interaction among the bolt surface and hole is modeled as a hard friction with friction coefficient 0.3 with the ability of separating after loading. Also, fillet welds are modeled as a prism with triangular section. Where a groove weld is applied, since the strength in this type of welding is like base metal, two connection parts are stuck together. To mesh the element, C3D8R element is used. The proposed connection n1 has the most rigidity values among semi-rigid connections. Reducing the number of connection bolts has more reducing impact on connection rigidity value, so that with the half thickness of upper and lower sheets, rigidity rate is reduced only 9%, but with the half number of bolts, rigidity rate is reduced about 64%. Also the connection n3 have lowest rigidity rate and its rigidity amount is in the class of bolted connection in seat angle to web angle.

Parametric Study of the Effect of Structure on Seismic behavior of Slope Topographic by Considering Soil Structure Interaction in Medium Stiffness Soils

A Erfani

Previous earthquakes have shown that topographic irregularities have significant impacts on the site seismic response and increasing structural damage by amplifying seismic responses. Studies on seismic behavior of slope topographic have shown that dynamic response of free field and soil-structure system is severely on the influence of topography shape and soil properties. Angle and height of slope, frequency of excitation, nonlinear behavior of soil and depth of bedrock are other parameters that affect on the response of the entire system. Furthermore the studies have shown that presence of structure adjacent to slope is very effective on variation of seismic behavior pattern of this topography but these studies are very limited. In this study the effect of existing structure adjacent to slope to seismic behavior pattern of slope topography have been investigated. The parameters that have studied in this article comprise slope angle and frequency content of excitation. The results show that the presence of structure adjacent to the slope, causes an increase to the response of free field and transmitting maximum response to distance away from structure position.

Numerical Modeling of Ground Vibrations Induced by Impact Pile Driving Using Finite Element Method

A Farshi Homayuon Rooz

Consecutive impacts of pile driver hammer on a precast pile head for pile installation in the ground is called impact pile driving. Nowadays, the widespread use of impact pile driving in pile foundations construction is undeniable; As a result, pile driving is the most common source of construction vibrations among the sources of producing ground vibrations. The ground vibrations during pile driving is the most important factor of limiting the use of this method. Thus, to avoid structural damages, acceptable prediction of ground vibration before any project implementation is necessary. For this purpose, numerical modeling is undoubtedly the most accurate, economical and fastest way; but up to now, correct modeling of pile installation process has been the main problem in numerical modeling of pile driving. This study aims to achieve better match of ground vibrations with field results compared to the previous numerical results in terms of peak particle velocity by modeling impact pile driving operation through ABAQUS finite element software from ground surface to a desired depth without considering previous researchers assumptions and considering the details of practical works.

On the Dynamic Behavior of Bridges Under Moving Loads

Gh Nouri

Due to increasing speed and mass of trains and vehicles, the errors arising from utilizing moving force method to obtain dynamic response of bridges cannot be neglected. In this paper, dynamic response of bridges under moving loads is studied. The bridge is modeled as simply-supported Euler-Bernoulli beam. Since in modeling moving loads by moving force method, inertial forces are neglected, this method is valid for a limited range of influential parameters (speed and mass). By considering inertial forces between the moving load and supporting structure, moving mass method can be utilized to extract dynamic governing equations. Numerical results reveal that by increasing speed and mass of the moving load, midpoint dynamic deflection of bridge obtained by two distinct methods differ considerably. For example, for mass ratio of 0.15 and speed ratio of 0.8, 11 percent difference is observed in midpoint dynamic deflection calculated by two aforementioned methods.