How to Design Concrete Structures for Retaining Aqueous Liquids According to BS 8007
Concrete structures for retaining aqueous liquids, such as water tanks, reservoirs, swimming pools, etc., need to be designed to ensure serviceability, durability and watertightness. One of the main challenges in designing such structures is to control the crack width and spacing due to thermal and shrinkage effects. In this article, we will explain how to use BS 8007:1987, Design of concrete structures for retaining aqueous liquids, as a guideline for designing concrete structures for liquid retention.
What is BS 8007:1987?
BS 8007:1987 is a British Standard that provides recommendations and guidance for the design and construction of concrete structures for retaining aqueous liquids. It covers both reinforced and prestressed concrete structures, and applies to both normal-weight and lightweight concrete. It also covers the design of joints, crack control, durability, inspection and testing.
BS 8007:1987 is based on the limit state design method, which requires the verification of two limit states: ultimate limit state (ULS) and serviceability limit state (SLS). The ULS deals with the strength and stability of the structure under extreme loads, while the SLS deals with the deformation, cracking and durability of the structure under normal service conditions.
Bs 8007 Crack Width Examples
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How to Design for Serviceability According to BS 8007:1987?
The serviceability design of concrete structures for retaining aqueous liquids aims to limit the deflection, vibration and cracking of the structure under normal service conditions. The deformation of the structure should not adversely affect its efficiency or appearance, or cause damage to other elements such as partitions, glazing or services. The vibration of the structure should not cause discomfort to occupants or possible damage to the structure or its contents. The cracking of the structure should be limited for aesthetic reasons or for watertightness.
According to BS 8007:1987, the serviceability design of concrete structures for retaining aqueous liquids involves the following steps:
Estimate the thermal and shrinkage movements of the structure due to hydration heat, ambient temperature changes and drying shrinkage.
Determine the degree of restraint imposed by supports, joints and adjacent elements.
Calculate the tensile stresses induced by thermal and shrinkage movements and restraint.
Provide adequate reinforcement to resist the tensile stresses and control crack width and spacing.
Check the deflection and vibration of the structure under service loads.
How to Estimate Thermal and Shrinkage Movements?
The thermal and shrinkage movements of concrete structures for retaining aqueous liquids depend on several factors, such as:
The type and properties of concrete, such as cement content, water/cement ratio, aggregate type and size, admixtures, etc.
The dimensions and shape of the structure, such as thickness, length, curvature, etc.
The curing conditions, such as temperature, humidity, duration, etc.
The exposure conditions, such as ambient temperature range, solar radiation, wind speed, etc.
BS 8007:1987 provides empirical formulas and tables for estimating the thermal and shrinkage movements of concrete structures for retaining aqueous liquids. For example:
The rise in temperature due to hydration heat can be estimated by: $$\\Delta T_h = \\fracQC \\left( \\frac1h + \\frac12k \\right)$$ where $\\Delta T_h$ is the rise in temperature (ÂC), $Q$ is the heat generated per unit volume of concrete (kJ/m), $C$ is the specific heat capacity of concrete (kJ/m/ÂC), $h$ is the thickness of the section (m), and $k$ is the thermal conductivity of concrete (W/m/ÂC).
The variation in temperature due to ambient temperature changes can be estimated by: $$\\Delta T_a = T_max - T_min$$ where 29c81ba772
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