Asian journal of civil engineering
Volume:17 Issue: 4, Jun 2016

Progressive collapse is a continuous spread and magnification of localized failure in structures, caused by an accidental load, resulting in a cascade of failure affecting a large portion of the structure. Although alternate path method is the most widely used method to increase the structural robustness of bare frame structures against progressive collapse, it should be further developed for other structures, and especially cable stayed bridges as they are highly sensitive to dynamic impact loading. This paper demonstrates modelling and analysis of a typical cable stayed bridge through two important analytical procedures, i.e., nonlinear static and nonlinear dynamic. Furthermore, the response of the structural model is discussed for multiple types of cable loss cases. Two different progressive collapse patterns are identified for nonlinear static and dynamic procedures as the dynamic unloading function is considered in the dynamic analysis procedure. The results also indicate a decrease in the possibility of failure progression of the cable stayed model when the location of the failed cables is closer to the pylon.

An economic hybrid base isolation system in the form of friction pendulum system (FPS) and pure friction (PF) sliding isolators is proposed. The effect of ground motion on the behaviour of a G+3 RC building mounted on hybrid isolators as well as on other support conditions are investigated analytically by using synthetic accelerograms that is compatible with the design spectrum of Indian standard (IS 1893 (Part 1): 2002) corresponding to the level of maximum considered earthquake in the most vulnerable seismic zone (PGA=0.36g). It is estimated that an average reduction of around 78% in maximum absolute roof acceleration is achieved with the combined sliding isolators compared to the conventional fixed base support which is at the cost of maximum relative base sliding displacement (average 32mm). The change in position of the isolators has almost the same results. It is also observed that the response reduction in roof accelerations for the FPS and Roller is at parity with that of FPS and PF (within 3%) hybrid isolators. Hence, the proposed hybrid system, i.e. FPS when combined with PF isolators can be economically and effectively used for developing countries without any residual displacement.

In this paper, the free vibration of the beam on elastic foundation is studied using finite element method. To this end, a two- node Timoshenko element is used for beam modeling. Each node in this element has a rotational and translational degree of freedom, which encompasses all four degrees of freedom. The displacement and rotational fields of this beam is selected from the third and the second order, respectively. Moreover, the shear strain of the element is assumed as a constant value. Interpolation functions for displacement field and beam rotation are explicitly calculated by employing total beam energy and it's stationary with respect to shear strain. Also, two-parameter elastic foundation model is used. In this method, the soil is modeled as a layer of Winkler springs with a shear layer on it. Next, by utilizing the interpolation functions, the stiffness matrices of beam and foundation, as well as their mass matrices are introduced; hence, the free vibration analysis on the elastic foundation is carried out. Finally, after conducting several tests, the high efficiency and accuracy of the proposed element is demonstrated.

Modern building products have the potentials to save energy and improve environmental impacts in comparison to conventional products. However, in order to reduce of the energy and environmental impacts of any building product, its materials and energy consumption must be evaluated over its entire life cycle. This study analyzed the energy consumption associated with the total life cycle of the building products. It reviewed the literatures and information provided in existing life cycle assessment studies and reports to develop a comprehensive analysis of the life cycle energy for the building products. The analysis comprised three main phases: manufacturing, transportation, and operation. The results confirmed that the life cycle energy analysis could assign the useful metrics for equal comparison the products types and reduced uncertainty throughout quantifying the energy consumption and environmental impacts of the entire life cycle of the building products. Moreover, the life cycle energy analysis provided the facility of continuing improvements to efficiency and operating lifetime of the building products.

An experimental study is carried out on concrete composed of two different types of coarse aggregates: crushed coarse aggregates (CCA) and rolled coarse aggregates (RCA). Aggregate shape, texture, and grading have a significant effect on the properties of the fresh and hardened concrete. This experimental study investigates the possibility to make a concrete with a binary natural coarse aggregates (crushed and rolled coarse aggregates). The experimental program reported herein was carried out to evaluate engineering properties of natural aggregates (crushed and rolled gravels) and dune sand-concrete mixtures in both fresh and hardened states. These properties were then compared to traditional concrete mixtures made with crushed gravel and dune sand to expand the beneficial use of rolled gravel concrete and underline its potential applications. Two series of coarse aggregates mixtures using crushed limestone gravel and rolled gravel have been investigated during this study; the first mixture (serie A: the first preliminary mixture proportioning method consists in obtaining the optimum mixture from a binary mixture of two fractions 3/8 mm and 8/15 mm of crushed limestone coarse aggregates at different percentages (0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90%). The obtained optimal mixture consists of 40 % crushed coarse aggregates (3/8 mm fraction) and 60 % crushed coarse aggregates (8/15 mm fraction). This optimal mixture of crushed coarse aggregates gave a minimal porosity and a maximal compactness. From this result the second concrete mixture formulation was prepared with two fractions (3/8 mm and 8/15 mm) of crushed coarse aggregates and one fraction (3/8 mm) of rolled coarse aggregates (serie B: the crushed coarse aggregates of 3/8 mm fraction was substituted by 3/8 mm fraction rolled coarse aggregates at various percentages 0%, 8%, 16%, 20%, 24% and 40% by fixing constant the percentage of 8/15 mm fraction crushed coarse aggregates at 60 % in all concrete mixtures prepared). The concrete with 40% of 3/8 mm fraction rolled gravel and 60% fraction crushed gravel showed a better performance than the control concrete in terms of the physical and the mechanical properties. This study allowed to better understand the influence of chemico-physical characteristics of coarse aggregates on the mechanical behavior of concrete. The inclusion of 3/8 mm fraction rolled coarse aggregates at replacement level of 40% and 60% of 8/15 mm fraction crushed coarse aggregates resulted in a increase in the mechanical strength of the concrete. The results show that, the use of 3/8 mm fraction rolled river gravel in concrete effectively improved the mechanical properties.

In this paper, acoustic emission (AE) test was used to assess concrete beams having a size of 100mm x 100mm x 400mm length with water-cement ratio of 0.50. Two types of beam were considered, plain concrete beams and short steel fiber-reinforced beams. There were three parameters used in acoustic emission test: AE hits, AE location, and AE energy.The total AE hits were divided into three percentile of AE energy all throughout the test. These are 100th, 25th, and 10th percentile of AE energy. This was done to differentiate significant AE signals with large AE energy from the less significant AE signals with small energy. It was found out that short steel fiber-reinforced concrete beams produced large number of total AE hits compared to ordinary concrete beams. The crack progression was clearly visualized at 10th percentile of AE energy.

As concrete is weak in tension, addition of extraneous materials has become an obvious choice to enhance the tensile strength properties of concrete. Steel fibres are added to enhance the strength properties of control mix. Change in either aspect ratio or geometric shape of the fibre has significant influence on the strength properties of fibre reinforced concrete. An experimental investigation was conducted to understand the influence of hooked end steel fibres on compressive, split and flexural strength properties of M30 grade concrete mix with fibre dosages of 0.50%, 1.00%, 1.25% and 1.50% of volume of concrete for the ages of 7, 28 and 90 days. It was found that though steel fibres did not influence the compressive strength to a great extent, it did influence split and flexural strength properties substantially. Increase in fibre dosage increased the compressive strength. Increase to an extent of 30% was found in split and flexural strength properties. Additionally, linear regression analysis was carried out among strength properties and R- squared value was found to be between 0.81 and 0.98.

In this paper, an optimization methodology proposed for the achievement of optimal (minimum) structural weight for flexible-base shear buildings under earthquake excitation. The underlying soil is considered as a homogeneous half-space which is replaced by a simplified 3-DOF system, based on the concept of Cone Models. Through intensive nonlinear dynamic analyses of buildings with consideration of soil-structure interaction (SSI) effect subjected to a group of artificial earthquakes, and using uniform distribution of inter-story ductility demand over the height of structures, an optimization procedure for seismic design of inelastic shear-buildings incorporating SSI effects is developed to achieve minimum structural weight. It is shown that the seismic performance of such a structure is superior to those designed by code-compliant seismic load pattern such that the optimized structures experience significantly less structural weight as compared with those designed based on ASCE/SEI 7-10 load pattern.

This paper presents a study on durability and dimensional stability of a Steel Fiber Reinforced Cementitious Mortar (SFRCM), and the results are compared with those of a common High Performance Concrete (HPC) mix.Common mechanical, durability, and dimensional stability properties of the hardened mortars and concrete are investigated by testing water absorption, water penetration, resistance to elevated temperature, thermal expansion coefficient, and drying shrinkage. The results reveal superior mechanical and durability performance of SFRCM in comparison to those of the HPC. However, there were some concerns about the performance of SFRCM exposed to elevated temperatures because of the low porosity and permeation. In addition, the higher thermal expansion coefficient and different shrinkage behavior of SFRCM should be considered in the design of structural elements.