Journal of Structural Engineering

Post-fire flexural and web-crippling behaviour of cold-formed steel built-up section beams

Aakash Patil — 2024-11-05

Worldwide, industrial constructions are frequently built using light gauge materials like Cold-Formed Steel (CFS) sections due to its lightweight and affordable design systems. One important aspect of building design and construction that must be considered is fire safety. The research involved studying flexural and web-crippling behaviour of CFS built-up beams subjected to controlled high-temperature conditions, then it was cooled to room temperature by furnace cooling method. Ten back-to-back built-up CFS sections were prepared to check structural performance after exposure to elevated temperatures of 500°C, 600°C and 700°C in an electrical furnace. The Finite Element (FE) modelling results are validated by experimental results. The validated FE models were then employed to carry out a comprehensive parametric study to investigate the effects of different web-to-thickness ratios, as well as sectional size to thickness ratio. The results demonstrated that the load carrying capacity and bending moment for flexural behaviour and web-bearing capacity for web-crippling behaviour of the CFS members can be significantly affected, (up to 56.04% and 37.26%, respectively with reference temperature) after exposure to elevated temperature. From the study, it is concluded optimizing the web height to thickness ratio is crucial for enhancing the structural performance of CFS components. However, higher temperatures resulted in a greater reduction in the load carrying capacity of the specimens.

Buckling behaviour of steel columns under elevated temperature

I. Meeramydeen — 2024-11-05

This paper presents experimental investigations on the behaviour of steel columns under elevated temperature. Axial restraints were applied to simulate the real-time boundary conditions, being part of a steel-framed structure. In the present study, two specimens, namely ISMB200-H1 and ISMB200-H2 were exposed to elevated temperature conditions by using 24kW and 7kW heaters respectively. The heating was carried out from room temperature to 800°C gradually, under a constant axial load applied through a specially fabricated loading frame. The critical temperature was estimated based on the point at which the specimen could no longer withstand the applied load. The applied load was significantly influenced by axial restraint, wherein additional stress was generated due to restrained thermal elongation in the axial direction. Two types of failures were observed at the end of experiments, namely (i) local mode of failure in the specimen ISMB200-H1 and (ii) global mode of failure in specimen ISMB200-H2 due to temperature concentration (maximum temperature) at top end plate and mid-height of the specimens respectively. The analytical studies were carried out with the expressions available in BS EN 1993-1-2, IS800:2007 and CSA S16:19 to have an understanding on load carrying capacity with increase in temperature. It is inferred that analytical studies provided comparable results on the load-bearing capacity of the specimen ISMB200-H2, which has failed by global mode.

Cracking behaviour of two-way reinforced concrete (RC) slabs supported on beams

R. Murugan — 2024-11-05

Two-way slabs are commonly used in Reinforced Concrete (RC) structures to resist gravity and lateral forces. Walls or RC beams and columns typically support these slabs. When designing slabs using the limit state method, strength and serviceability criteria must be met. Even though current codes have established design methods for strength limit states, they lack well-established design methods for serviceability limit states, particularly crack width calculations in two-way slabs. Although a few studies from the literature have examined the cracking behaviour of RC two-way slabs in scaled specimens, those that investigate RC two-way slabs supported on beams have not yet been reported. This paper delves into the complete cracking behaviour of two-way slabs using an experimental investigation on four prototype RC two-way slab systems supported on beams, with varying slab thicknesses and reinforcement spacing. The study demonstrates that the cracking behaviour of RC elements under two-way bending differs significantly from that under one-way bending. The current research thus reveals the need for the development of a different analytical expression for crack width estimation in two-way slab systems. The findings of this research work could be valuable as an input parameter in developing code provisions for crack width calculation in two-way slabs.

Determination of mechanical properties and environmental impact assessment of concrete containing industrial wastes

S. Varadharajan — 2024-11-05

The Imperial Smelting Furnace Slag (ISF Slag) is a byproduct of zinc mining. The ISF slag contains hazardous elements such as lead and zinc and a thorough treatment before its disposal is required which demands a significant investment of time, money and effort. Also, increased construction activities produce large amounts of Waste Marble Powder (WMPs) and Construction and Demolition (C&D) waste which results in severe environmental degradation. The first goal of this paper is to propose a pathway for the safe disposal of these wastes by partially substituting them in concrete in place of Fine and Coarse Aggregate (FA & CA). Secondly, this research aims at to identify an optimal combination of these wastes for improved strength and environmental benefits. The results of experimental study shows that a combination of, a) 10% WMPS and 15% ISF slag, b) CA replaced by 10% C&D waste in concrete with addition of 1% Hooked Steel Fibers (HSF) (by weight of cement) exhibits best strength enhancement of 13.26%, 16.52%, and 18.43% in compression, tension, and flexure respectively. The environmental impact assessment using Recipe mid-point and end-point analysis shows reduction of particulate and greenhouse gas emission by 35.5% and 41.8%, respectively.

The effect of alkali activator solution on the consistency and setting properties of sustainable geopolymer paste with fly ash and GGBS as blended binder

K. Bavithradevi — 2024-11-05

The present study examines the effect of Alkali Activator Solution (AAS) on the consistency and setting properties of the blended binder geopolymer pastes considering the following parameters: (i) geopolymer pastes produced with three different alkali activator ratios (sodium hydroxide: sodium silicate) 1:1, 1:2 and 1:3, (ii) geopolymer pastes produced considering four different molarities of Sodium Hydroxide Solutions (SHS) 2.5M, 5M, 7.5M, and 10M, and (iii) geopolymer pastes produced as blended geopolymer pastes with varying blending ratios of FA and GGBS 30:70,50:50 and 70:30. The consistency and setting characteristics of geopolymer pastes for the 36 different mix combinations were studied. The finding revealed that the molarity of SHS and the ratio of AAS are influencing the consistency and setting characteristics of the proportionately blended FA and GGBS-based geopolymer paste. The increase in the AAS ratio has minimal effect on the consistency of geopolymer pastes except for the geopolymer paste produced with 10M of SHS. The initial and final setting times of geopolymer paste decrease with an increase in the ratio of AAS. The flash setting of geopolymer paste was observed for mixes J3, K3, and L3 which are produced with 10M of SHS and an AAS ratio of 1:3. Microstructural studies such as Scanning Electron Microscopy (SEM) analysis and Fourier Transform Infra-Red Spectroscopy (FT-IR) analysis were carried out. The formation of ettringite was seen in SEM images of FA-rich mixes of geopolymer paste activated with 2.5M molarity of NaOH.

Condition assessment of historic masonry structures: a case study

Bhaskar Sangoju — 2024-11-05