Flexural behavior of cold-formed steel concrete composite beams

Flexural behavior of thin walled steel-concrete composite sections as cross sections for beams is investigated by conducting an experimental study supported by applicable analytical predictions. The experimental study consists of testing up to failure, simply supported beams of effective span 1440 mm under two point loading. The test specimens consisted of composite box and channel (with lip placed on tension side and compression side) sections, the behavior of which was compared with companion empty sections. To understand the role of shear connectors in developing the composite action, some of the composite sections were provided with novel simple bar type and conventional bolt type shear connectors in the shear zone of beams. Two RCC beams having equivalent ultimate moment carrying capacities as that of composite channel and box sections were also considered in the study. The study showed that the strength to weight ratio of composite beams is much higher than RCC beams and ductility index is also more than RCC and empty beams. The analytical predictions were found to compare fairly well with the experimental results, thereby validating the applicability of rigid plastic theory to cold-formed steel concrete composite beams

Self-compacting concrete containing granite powder

The potential of producing SCC (self-compacting concrete) using granite powder (GP) which is a waste material was investigated. Eight trials were carried out by incorporating granite powder at 20 and 30 (GP20 and GP30) of the total powder content in SCC. Eight SCC trials were carried out by incorporating 20 and 30 fly ash (FA20 and FA30) with total powder content. Since the water content in all the mixes was kept constant at 180 kg/m 3, the dosage of superplasticiser was increased as the total powder content increased. SCC mixes incorporating 20 and 30 granite powder achieved fresh concrete properties comparable to those of the fly ash based SCC mixes. Additionally, they hardened faster and had higher compressive strengths at 3-day than FA-SCC mixes. The 56-day compressive strengths of FA-SCC show an increase in strength in the range 13-23 indicating strength development after 28 days

Comparative BehaviourOf High Rise Buildings With DiagridsAnd Shear Wall As Lateral Load Resisting System

Structural systems for tall buildings have undergone dramatic changes after observing that conventional Rigid Moment Resisting frames alone, the earlier predominant structural system for steel or concrete tall buildings was inefficient in resisting lateral loads. The intensity of the seismic and wind load increases with increase in height of the structure and demand the use of an additional Lateral Load Resisting System (LLRS) for enhancing performance. The LLRS for high rise buildings depend largely on the height of the building. Some of the LLRS that are currently used are Shear Wall (35m), Tube Structures- Frame tube (80m) and bundled tube (100m), Diagrid (100m), Super frames (160m) etc. Diagrid is a technique typically used for constructing large steel buildings by creating external triangular structures with horizontal support rings. The Diagonal members in Diagrid structural systems can carry gravity loads as well as lateral forces. In the present study, the behaviour of Diagrid structures in terms Lateral sway is compared with that of building with shear walls to evaluate the efficiency of Diagrid structures. A 45 storey steel building with a plan area of 36×36m and triangular pattern for diagonal members with a Diagrid angle of 63? is considered. The variations considered are density of Diagrid as 3, 4 and 6 and length of Shear wall, each 6m and 12m along X and Y directions at the corners of the building. Seismic analysis is carried out for seismic Zone V considering various load combination as per IS Codal provisions using SAP2000 V-15.It is found that Lateral displacements of a Diagrid structure are much less than that of shear walled structures proving its efficiency. The study also determines the optimum density of Diagrids considering the structural behaviour and practical considerations.&nbsp

Seismic analysis of 3-D building frame with masonry infill and steel bracings as lateral load resisting systems

Lateral Load Resisting System (LLRS) which will supplement the behavior of moment resisting frames is important for high rise structures to resist the lateral load. Natural phenomenon like earthquake causes damage to or collapse of buildings if not designed for lateral loads resulting due to Earthquake. Shear walls, Infill frames and Steel bracings are some of the LLRS commonly used. An attempt is made in the present study, to analyze the structural behavior of 3-dimensional (3D) single-bay-four-bays, 10 storey basic moment resisting RC frames when provided with Masonry infill and Steel bracings as LLRS. The detailed investigations are carried out for zone V of Seismic zone of India, considering primary loads and their combinations. Four models are analyzed consisting of one basic moment resisting RC frame and other three include basic moment resisting RC frame with Masonry Infill (idealized as diagonal compressive strut), External and Internal Steel Bracings. The results obtained from the linear dynamic analysis are thoroughly investigated for maximum values of joint displacements, support reactions, column forces, beam forces, forces in truss elements and dynamic properties. Better resistance to lateral load of the frames in the presence of LLRS is observed from the results obtained. Copyright © 2008 by the International Institute of Informatics and Systemics

Effect of soil flexibility on dynamic behavior of building frames resting on strip foundation

The effect of soil flexibility is generally ignored in seismic design of buildings. The design is generally carried out based on the results of dynamic analysis considering fixed base condition. Flexibility of soil causes lengthening of lateral natural periods due to overall decrease in lateral stiffness. Such lengthening may considerably alter the seismic response of the building frames. It is therefore, necessary that the dynamic inter relationship between soil and structure to be taken into account in the seismic analysis of structures. In order to evaluate the seismic response of a structure, at a given site, the dynamic properties of the combined soil structure system must be established. Due to the differences in responses of a rigidly supported structure and elastically supported structure, it is essential to study the effect of soil flexibility on structure for safety and economy. The seismic load acts during a very small interval of time. Hence, during the action of such loads, instead of consolidation settlement, the instantaneous settlement is expected to occur. This behavior of soil can be conveniently simulated using a set of elastic springs. This study has been carried out for numerous building frames resting on strip foundations and comparison between the nature of change in lateral natural periods and base shears due to the incorporation of soil flexibility relative to that at fixed base condition has been presented. Such study may help to provide guidance to assist more accurately the seismic vulnerability of the building frames resting on strip foundations and may be useful for seismic design. © 2010 ASCE

Contribution of existing lateral load resisting systems in seismic response of multistory structure

Using an appropriate structural system is critical to good seismic performance of buildings. While moment-frame is the most commonly used lateral load resisting structural system, addition of other structural systems like structural walls, frame-wall system improve the seismic resistance. Structural system chosen should be suitable for good earthquake performance, with vertical and horizontal members of lateral load resisting system (LLRS) that can carry earthquake effects safely during strong earthquake shaking. Studies on real structures, practically adopted are negligible. Present work deals with the comparison of seismic performance of the structural system under consideration with existing features (Lift core RC wall & Infill effect along the boundary walls) as LLRS in the building using response spectrum and time history method. © 2018 Associated Cement Companies Ltd. All rights reserved

Sorptivity behaviour of self compacting concrete made with basalt as aggregate

In recent years the strength and durability of structures are given equal importance due to the premature deterioration of RCC structures which assumed serious proportions. The durability of a concrete structure is closely associated with the permeability (Kollek 1989) of the surface layer, the one that should limit the ingress of substances that can initiate or propagate possible deleterious actions. This paper deals with the comparison of Sorptivity parameters of SCC produced for three different cementitious contents of 400kg /m3, 500kg/m3, & 600kg/m3 of SCC, using two types of aggregates Basalt & White Granite. Six mixtures of SCC investigated were designed using Absolute Volume method without the use of VMA with a constant quantity of 180 litres of water per cubic meter of SCC which results in water binder ratio of 0.3, 0.36 & 0.45. Dosage of admixture was adjusted to get the required rheology as per EFNARC Specifications. Compressive Strength and Sorptivity (durability characteristic), were tested as per relevant codal provisions. From the results of 6hr and 8 day Sorptivity of SCC as per code, it may be concluded that mixes of SCC made with two types of aggregates showed lesser resistance at 400 kg/ cum cementitious content and better resistance at cementitious contents of 500 and 600 kg/ cum of SCC for both aggregates, with Basalt showing higher resistance than White Granite. This may be due to the fact that increase in cementitious content (fines) and self compacting property of SCC reduces the void and increases packing hence results in decrease the sorption. © 2010 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved

Analytical study on behavior of External Shear Wall and Internal Shear Wall as lateral load resisting systems for retrofitting a ten storey building frame

Earthquakes are natural phenomena under which disasters are mainly caused by damage to or collapse of buildings and other man-made structures. Many existing buildings lack the seismic strength and detailing requirements as per standard codes of practice. An existing structure may need upgrading or retrofitting if the structure was initially not designed and constructed to resist an earthquake i.e. designed only for gravity loads. The present study consists of a comprehensive three-dimensional elastic analysis using Response Spectrum Method (RSM) of a ten storied building structure wherein External Shear Walls and Internal Shear Walls are considered as Lateral Load Resisting Systems (LLRS) as possible measures of retrofitting of structures. The behavior of the building in which LLRS are employed is compared with moment resisting Bare frame (without any LLRS). The building located in zone V (Most sever) of seismic zones of India, is subjected to seismic loads, non-seismic loads and their combinations to arrive at the critical deformations and forces in the structure. The following 3D frame models are considered for analysis. 1. Basic Single bay - three bays Moment Resisting Frame. 2. Frame as in (1) with External Shear Wall. 3. Frame as in (1) with Internal Shear Wall. The study reveals that both External Shear Walls and Internal Shear Walls effectively reduce the lateral deformation due to earthquake loading but latter are more effective as LLRS. However External Shear Walls can be employed when it is difficult to disturb the interior of the building during retrofitting. © 2012 Taylor & Francis Group