Abstract:
In Prestressed concrete, the initial compression is applied to the concrete before applying
any external load so that stress from external loads is counteracted in a favourable way.
Camber in precast prestressed slab panels can be defined as the upward deflection that is
caused due to the moment caused by the eccentric prestressing force. Excessive camber
development in precast prestressed slab panels can lead to several problems such as
needing extra amount of topping concrete meaning extra cost and extra dead load. In
addition, cracking of top surface of slab leads to durability problems. Therefore, accurate
prediction of camber is essential to minimize these problems. The objective of this
research is to identify the causes for the difference between design and actual camber and
to propose suggestions to minimize excessive camber in precast prestressed slab panels.
To achieve the research objective, a literature review was carried out to identify camber
calculation methods in precast prestressed slabs and to identify the reasons for difference
between calculated and actual camber. Then did manual calculations for designing of
sample precast prestressed slab panel. Electronic strain gauges were installed to high
strength strands to measure the strain developed in the strands during stressing and
destressing processes and obtained the data logger readings. Then comparative analysis of
literature review findings, theoretical calculations and practical observations were done,
and the conclusion was derived based on above analysis results. From the recalculation
process by using the material properties and parameters obtained by experimental data, it
is shown that it is adequate to use 5 number of strands instead of 6 number of strands.
From the experimental values obtained from concrete cylinder tests, the actual Modulus of
Elasticity in concrete used is lower than the values considered in design. When the
Modulus of Elasticity of concrete decreases, the upward deflection also increases. Because
of excessive camber development we had to put extra amount of topping concrete
thickness to maintain the minimum topping concrete layer thickness of 75 mm and to
maintain levelled floor surface. This increases extra 5.27% of topping concrete material
cost.
Stress releasing process of strands was done one by one and is not symmetrical. Therefore,
the stress at strands varies during the releasing process. Due to this reason, there can be a
twist in the precast prestressed slab panel and the camber value also varies along a cross
section considered. Therefore, it is suggested to release all strands simultaneously.
Citation:
Gamage, M.D.D. (2021). Study and analyse the excessive camber development in precast prestressed slab panels [Master's theses, University of Moratuwa]. Institutional Repository University of Moratuwa. http://dl.lib.uom.lk/handle/123/20366