AHSANULLAH UNIVERSITY OF SCIENCE & TECHNOLOGY

PRE-STRESSED CONCRETE LAB

SUBMITTED BY : SABRINA SHAHRIN ZEBA

ROLL : 10.01.03.124

section : c

CE-416

COURSE TEACHER : MR. GALIB MUKTADIR & SABREENA N.MOURI

*Temperature variations and shrinkage are the most important causes of structure deformation

*It causes deflection,cracks,and creeps in concrete

• Change of pore water content due to temperature variations like drying process causes volume changes in structure ,this phenomenon is called shrinkage

• In shrinkage mainly loss of water consumed by hydration reaction

• change in volume during hardening resulting shrinkage stress

• Rapidly drop of temperature between day and night can cause contraction in a concrete length ie. shrinkage , which is sufficient to causing cracking

• Crack produce when tensile stress>concrete tensile stress

As concrete weak in tension ,the resulting stress of shrinkage produce cracks known as hairline cracks

• This cracking decreased load carrying capacity

• Reducing strength with time under constant stress and temperature known as creep

• At high temperature atoms are dislocated,which causes creep deformation

• It is a tendency of a solid material deform permanently under the influence of stress ,which is generated by temperature effect

• This deformation is function of exposure time and exposure temperature

• Moisture content available in creep

• if the stress is applied long enough, the material may gradually deform until it breaks

• In prestress design temperature and shrinkage effect known as loss

• Creep loss and shrinkage loss are the example of them

• To get the accurate effective prestress this loss should be calculated

• Effective Prestress= Initial Prestressing Force - All Losses

• Loss due to creep: ∆fc=(Cc-1)n fc N/mm² , Cc=co-efficient of creep

• Loss due to shrinkage: ∆fc=Es s N/mm² , s=co-efficient of shrinkage

*Distribution reinforcement reducing this effect

*When concrete tends to shrinkage such reinforcement resist the contraction

*If crack prodused will be smaller width and more evenly distributed to the concrete

*This reinforcement provided perpendicular to the main reinforcement bar,used in one way slab

*This reinforcement requires in floor and roof slab

*using high paste concrete with proper amount of water and cement reduce this effect

Temparature and shrinkage effect can be minimize but it can not be remove permanently so, proper admixtures,appropriateratios must be taken for reducing this effects.Adequate building codes with balanced design can provide safe building.