Journal of the Structural Engineering and Geotechnics
Volume:5 Issue: 1, Winter 2015

Past earthquakes have demonstrated that old RC bridges may be seismically vulnerable. Bridge responses during the last decades illustrated the necessity of the seismic assessment of bridges especially those which were designed with old codes. In this research an existing concrete bridge representative of the most common bridges in the highway system in Iran are studied. Push over and nonlinear time history analyses using refined 3-D structural models are performed for each sample. Bridge structural systems are identified and quantified to establish a set of earthquake-site-bridge samples. The superstructure was assumed to remain elastic and the nonlinear behavior in piers was modeled by assigning plastic hinges in columns. The soil flexibility was considered by using elastic spring elements. Displacement ductility and peak ground acceleration (PGA) were selected as seismic performance indicator and intensity measure, respectively. Ten time history records from the past earthquakes were selected. They were scaled and applied incrementally to the 3-D model to evaluate seismic performance of the bridge. Furthermore, bridge damage states were defined and the probabilistic characteristics of structural capacity corresponding to each damage state were established. Then, the conditional probabilities of specific structural demand to exceed the structural capacity were computed and the results were displayed as fragility curves.

Field observations of the incurred damages to the buildings and bridges due to earthquakes in near field show there are various failure modes which are in relation to the forces caused by vertical component. While vertical component of earthquake for ordinary buildings in most seismic regulations and standards is not considered. Therefore, in the current study the effects of vertical and horizontal components of earthquake on regular and mass asymmetric structures are investigated simultaneously. The study considers a model of one-story structure with 3 degrees of freedom, lateral displacement, torsional displacement of roof level and vertical displacement, on a rigid foundation. It is concluded that for all such structures in the near-fault zones, the effect of vertical component must be considered. In case of stiff structures, the effect of the force on displacement of such structures is of importance and the effect of vertical component can be disregarded. The use of vertical design response spectrum to calculate the vertical forces caused by near field earthquakes is also recommended.

This article considers the seismic behavior of beam-to-column joints in steel frames for different bolt arrangements by using of finite element modeling. As the most important beam-to-column joint type, the beam-to-column joints with end-plate is chosen for the analysis. Four different specimens have been analyzed. These models had some differences such as bolt arrangement and the presence or absence of end-plate stiffeners. Design of bolts arrangement and stiffeners have been done based on the AISC standards. Two vertical bolt arrangements, with or without stiffener and two other models with horizontal bolt arrangement, with or without stiffeners have been considered. Different aspects such as energy absorption, ductility, initial stiffness and effective stiffness for all specimens have been compared. Finally effect of pre-stressing of all specimens has been assessed. As a result, comparison between vertical bolt arrangement and horizontal bolt arrangement has shown that the vertical bolt arrangement is more advantageous, especially in energy absorption

Response modification factor (R-factor) is one of the seismic design parameters to consider nonlinear performance of building structures during strong earthquake. Relying on this, many seismic design codes led to reduce earthquake loads imposed to the structure. The present paper tries to evaluate the R-factors of conventional concentric braced frames (CBFs) and special moment frames (MRFs) in duplex steel buildings with level difference in their floors. Since, the R-factor depends on ductility and over strength, the incremental nonlinear static analysis, push over analysis, has been performed on 4, 7 and 10 storey building models with three floor level differences and including CBFs and special MRFs systems in x and y directions of buildings respectively. The results showed that the R-factors for CBFs system in duplex buildings were higher than ones in conventional buildings without floor level differences while for MRFs system it was found that on 4 and 7 storey duplex buildings, the R-factors were decreased and with the increase in building height to 10 storey, they were increased compared to conventional models.

In the construction process of a plastic concrete cut-off wall, concreting is usually performed using the termie pipe method. In this method, concreting is performed from the lowest point in the excavated trench (containing the slurry) using a funnel and the pipe connected to it. The concrete poured in the funnel gradually settles in the panel through the termie pipe which is beneath the slurry and the end of the pipe has always been in the concrete. Because of its unit weight which is less than that of the concrete, the slurry goes up and the height of its column reduces. As the construction continues the length of the termie pipe is cut down so that the remaining operation is carried out more easily. In this process there are three types of flows to be considered: concrete flow in the termie pipe, concrete flow in the panel and slurry flow in the panel. Using the fundamentals of hydraulics, this paper tries to study the interactions among these fluids. It also examines the influential factors in removing the bentonite jelly in order to provide the plastic concrete with homogeneity and consistency (slump 22-16 cm) in primary and secondary panels of cut – off wall as a most reliable water tightening system in most dam foundations.

In this paper a laboratory study has been carried out on the effect of changing the type of soil filling cylindrical reinforcing elements from SM to GM on behavior of sandy soil. In this study the primary tests for evaluation of the impact of reinforced sand and gravel columns with diameters of 5 cm and heights of 15 cm subjected to vertical stresses of 50, 100, and 150 KPa were carried out in a large-scale direct shear apparatus (300×300×150 mm). Results showed that the shear stress and settlement of the reinforced sample with geogrid and a gravel column increases by 45.4% and decreases by 23.9% respectively compared to the non-reinforced sample.