Rapid development of the big cities and suburbs around the world in the last century has created a situation in which the main focus of urban rainwater runoff is the disposal of the stormwater as quickly and efficiently as possible to the disposal site, without considering the water quality at outfall. This has contributed to the decline of water quality of the rivers, lakes and other receiving bodies. Whilst some progress has been made towards the reduction in pollution at the source, it is the non-point sources of pollution entering the water runoff system at various points and from different sources that is the most difficult to monitor and manage.
Earthquake-resistant structure systems should be designed to stand large deformation to absorb and attenuate imposed energy due to an earthquake while providing sufficient stiffness to transfer the forces to the base without collapse. Knee Braced Frames (KBF), which involves added additional diagonal elements to a frame to increase its ability to withstand lateral loads, is suggested by several researches. In this study, the seismic performance of KBFs are evaluated and compared with Eccentric Braced Frames (EBF). Nonlinear static analyses were utilized for seismic evaluation and comparison between the mentioned frame systems. Three steel structures of 5, 10, and 15-story were numerically modeled, and the seismic parameters such as lateral stiffness, inter-story drift, ductility, and response modification factors were calculated for each structure system. It was observed that using KBF systems resulted in a reduction in intersotry drifts compared to EBFs. KBF systems show more stiff responses in comparison with EBFs and they presented much more stiff response by reducing the knee element length. The KBFs have more ductile behavior in comparison with EBFs, although base shear in KBFs is less than EBFs.
The progressive collapse phenomenon refers to a chain of damages in a structure where all or a large part of the structure is destroyed by an initial local collapse in it, which can lead to very disastrous results. Therefore, the prevention of progressive collapse has become a necessary action in the design and analysis of buildings and it is vital to investigate this topic more accurately. This study aims to present a proposed pattern in the configuration of braces at the height of a high-rise steel building for reducing the probability of progressive collapse. In this regard, the vertical displacement of 18-story structure with four scenarios of column removal and five concentric bracing patterns including V, Inverted V, X, discontinuous X-bracing at height, and a combination of Xbracing in the side spans and discontinuous X-bracing at height in the middle spans are investigated and compared. In this study, the Alternative Path Method (APM) is used based on the GSA guideline for the analysis of progressive collapse. The results of this research showed that the use of X-bracing in the side spans and discontinuous X-bracing in the middle spans in nonlinear static and dynamic analyses performed better in reducing the probability of progressive collapse than other bracing configurations. Finally, it is recommended to use discontinuous X-bracing at the height that would place the bracings in one direction and providing alternative paths for force transferring in the structure.
The precise study of connections performance in a steel structure is important. End plate connections are commonly used in steel structures. In this research, the cyclic behavior of cantilever beam connection to the endplate column under cyclic loading has been evaluated. In the calculations, all of the parameters affecting the behavior of this connection have been investigated and solutions are proposed to reach the maximum connection capacity. Two general models of connecting beams to different columns have been considered for the research with beams of 30 and 40 centimeters depth. The end plate thickness, end plate shape, column thickness, strength or the material of the bolt, necessity of using the continuity plate, double and gusset plate, are the parameters that were considered in the analyzes. According to the results of this study, the use of a thin end-plate causes localized buckling in the plate. The use of continuity plates is very important and prevents local buckling in the panel zone. It is also necessary to use a double plate if the column web is thin. Also, the use of gussets improves the flexural strength of the section.
The presence of web openings in castellated beams introduces different modes of failure at the perforated sections such as excessive stresses in tee-sections, excessive stresses in mid-depth of the web post, web-post buckling, developing plastic Vierendeel mechanism. This paper presents nonlinear behavior of castellated beams under moment gradient loading and investigates the effect of beam length and braced length on moment-rotation behavior and ductility of this type of beams. Accuracy of finite element models of plain-webbed beams is evaluated comparing moment-rotation behavior and failure mode of other researchers' numerical models and cleared a satisfactory accuracy. Rotational capacity of castellated beams, derived from numerical modeling, is compared with corresponding I-shaped plain-webbed steel beams and it is cleared that for the short beams, web openings reduce energy absorbance and plastic moment capacity of the beams more than long ones.
Final lining in mechanized excavation includes the precast concrete segments. These segments are designed for applied loads during construction, moving, depot, assembling in the tunnel and service loads that are affected by earth conditions. One of these loads that are applied to the segments after assembling in the ring, are TBM jack loads especially when the TBM should excavate squeeze zones with single mode. As the jack pad section is smaller than the segment section, it causes splitting loads in the segment. Symmetric prism method is an approximate solution to evaluate these forces. In this paper, calculated results by this method are compared to that of numerical solution by ANSYS software. It shows 10-20 percent difference between numerical and analytical results.
In this study, A reinforced concrete (RC) reference specimen with compressive strength of 250 kg/cm 2 and the weak RC specimen for seismic rehabilitation with compressive strength of 150 kg/cm2 were examined in two types of structures with 6 and 12-stories. The link beam lengths of 50, 80, and 100 cm have been used in 6 and 12-stories prototypes under the effect of 7 earthquake records. The nonlinear dynamic analyses are performed. Then, The behavior of the link beam depends on its length. For short link beam lengths, shear behavior is serious, then for medium lengths, shear-flexural behavior is important, and finally, long lengths will have flexural behavior for the beam. In eccentrically braced frames, the details of the link beam and the fit of the other members must be done in such a way as to ensure its proper ductility. According to the obtained results, the performance of short link beams is much better than long link beams, and short link beams provide more energy dissipation and, at the same time, more ductility. Therefore, in the design of the link beam, mainly the shear of the link beam is considered as a ductile component. The axial force in the link beam, which is due to the application of lateral load to the structure, reduces both the bending capacity and the inelastic deformation capacity of the link beam, so it can be explained that in steel eccentric braces, the link beam is symmetrical between the two main components of the brace and it can affect the strength of the structure against lateral loads.
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