For contraction joints, it may be possible to design a concrete structure without any
contraction joints. By using sufficient steel reinforcement to spread evenly the crack width
over the span length of the structure, it may achieve the requirement of minimum crack
width and cause no adverse impact to the aesthetics of the structure. However, it follows
that the amount of reinforcement required is higher than that when with sufficient
contraction joints.
For expansion joints, the consequence of not providing such joints may be difficult to cater for. For example, a concrete structure has the coefficient of thermal expansion of 9x10-6 /oC and a Young’s modulus of 34.5kN/mm2. With an increase of temperature of 20oC and it is restricted to free expansion, then the structure is subject to an axial stress of 6.21MPa. If the structure is very slender (e.g. concrete carriageway), buckling may occur. Therefore, the structure has to be designed to take up these thermal stresses if expansion joints are not provided. However, for water retaining structures, most of them are not affected by weather
conditions because they are insulated from the water they contain internally and soil backfill that surround them. Therefore, it is expected that a smaller amount of thermal movement will occur when compared with normal exposed concrete structure. Consequently, expansion joints may be omitted in this case with the view that the compressive stress induced by thermal expansion toughens the structure to limit the development of tensile stress.
But i think we must use expansion joints for other requirements, like due to changes in level of foundations or change in properties of soil to avoid differential settlement.
Also, there is expansion joints for seismic requirements to avoid hammering between adjacent buildings.
- Badges
- Science topic
- Similar topics
- Philosophy
- Moral Philosophy
- Free Will