Consistent strut-and-tie modelling of deep and short beams and hollow-core slabs at ambient and elevated temperatures

Abstract

Strut-and-tie model (STM) has been widely incorporated in different codes of practice due to its accuracy and consistency in designing Discontinuity-regions.Discontinuity-regions refer to regions where the strain distribution is significantly non-linear and traditional shallow beam theory does not apply. Application of STM to Discontinuity-regions or members comprising entirely of Discontinuity-regions, such as reinforced concrete (RC) deep and short beams, corbels, beam-column joints, etc., under ambient condition has been well verified by different researchers.However, the feasibility of applying STM to deep and short beams subjected to fires or to prestressed precast concrete hollow-core (PCHC) slabs with non-uniform cross-sectional properties and no web reinforcement at ambient temperature have hardly been investigated. Besides, there is a lack of experimental test results of heated short beams with/without axial restraint and fire-exposed deep beams under unequal and/or unsymmetrical loading arrangement. Therefore, experimental data is needed for verification of the proposed STM approaches for deep and short beams at high temperatures. In addition, there are challenges in selecting an optimal STM for RC deep beams with variations in load configurations such as the load magnitude, equality, symmetry and load combinations. Hence, research is needed to develop a direct approach for determining a suitable STM geometry to simplify the analysis procedure for engineers.To bridge the gaps, the present research programme is conducted to:(1) Examine experimentally structural fire behaviour of axially-restrained and unrestrained short beams, with shear-span-to-effective-depth (a/d) ratio ranging from 1.50 to 2.50, followed by the development of a general STM-based approach for simulating the response of short beams subjected to fire.(2) Conduct analytical and experimental studies on RC deep beams under combined effects of load inequality, load asymmetry, and elevated temperatures.(3) Develop and validate a refined and direct STM approach for both symmetricallyand unsymmetrically-loaded deep beams at ambient temperature. Summary viii (4) Establish and verify a STM approach to predict the web-shear capacity of PCHC slabs at ambient temperature.To achieve the research objectives, two series of tests were conducted on seven short beams (Series I in Chapter 3) and six deep beams under elevated temperatures (Series II in Chapter 4). The first series was to investigate experimentally the effects of a/d ratio and thermal-induced axial restraint on structural fire behaviour of short beams, while Series II was for unsymmetrically-loaded RC deep beams at elevated temperatures. The experimental data were utilised to establish proposed STM approaches for assessing the shear resistances and fire durations of deep and short beams when exposed to fires. Based on the experimental and analytical studies, it was found that: (i) The presence of elevated temperatures altered failure model of deep and short beams to a less brittle failure m...