A study on the construction process (Precast concrete, In-situ cast concrete, Shoring, Underpinning)
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A study on the construction process (Precast concrete, In-situ cast concrete, Shoring, Underpinning)
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A study on the construction process (Precast concrete, In-situ cast concrete, Shoring, Underpinning)
- 1. A Study on the Construction Process Precast Concrete In-situ cast Concrete Shoring and Underpinning
- 2. Introduction Precast concrete In-situ cast concrete Shoring Underpinning
- 4. What is Precast Concrete? • Cast into specific shapes at another location • Developed in the late 1960s • First use: stair treads, coping, lintels, and window sills • Known for its high quality architectural products
- 5. Characteristics • Great accuracy and high quality • Additional features: reinforcing, moles, anchor bolts, etc • Characteristics controlled by different materials • Reinforcement: Conventional reinforcing or prestressed steel
- 6. Manufacture • Casting beds used • High strength steel strands pretensioned • Transverese bulkhead seperators inserted • Additional reinforcement added • Concrete poured and vibrated • Cured with live steam or radiant heat
- 7. Slabs • The most standardised precast elements • Includes solid flat slab, hollow core slab, double tee slab, and single tee slab
- 10. Double tee slabs
- 11. Single tee slabs
- 12. Beams • Made in different sizes • Rectangular beams, L shaped beams, inverted T beams and AASHTO beams
- 13. Wall panels • Prestressed or conventional reinforcement • Used as load bearing walls • Includes solid wall panels, hollow core wall panels and tee wall panels
- 16. Tee wall panels
- 17. How are precast buildings put together? Double tee slabs supported on frame of columns and girders
- 18. Hollow core slabs supported on load bearing walls
- 19. Double tee slabs supported on load bearing walls, columns and inverted tee beams
- 21. What is in-situ cast concrete? • Concrete that is cast into forms on the building site • Any shape that can be formed can be cast • Certain types of concrete elements cannot be precast, and can only be cast in-situ
- 22. Selecting an in-situ cast concrete framing system • Are the bays of the building square or nearly square? • How long are the spans? • How heavy are the loads?
- 23. In-situ Concrete mix • Appropriate concrete properties designed • Appropriate mix design developed • Mixing, transporting and handling coordinated with placing and finishing
- 24. In-situ concrete placement • Should not be placed more rapidly than it can be spread • Deposit as near as possible to the final position • The concrete is placed in forms and consolidated
- 25. Curing • Satisfactory moisture content and temperature required • Concrete in formwork is protected from drying out • Curing compounds and treatments prevent loss of moisture • Large surface areas problematic during curing
- 26. Advantages • Easy transportation of wet concrete • Flexible when it comes to geometric shapes • Relatively easy to do late changes to structure • Structure becomes monolithic
- 27. Disadvantages • Produced in an unprotected environment • Additional time required for drying out process • Requires more temporary work • Complex process with many inputs and flows
- 28. Shoring
- 29. What is shoring? • Construction of a temporary structure to support an unsafe structure
- 30. When do we need shoring? • When walls bulge out • When walls crack • When an adjacent structure needs to be pulled down • When openings are to be newly made or enlarged in a wall • During construction
- 32. Raking shores • Rest upon the ground and support the wall by being inclined against it
- 33. Using raking shores • Size of the raker decided on anticipated thrust from the wall • Center of the raker and wall should not meet at floor level • Shoring may be spaced at 3 4.5m • Wedges should not be used on sole plates • For tall buildings, rider raker can be used
- 34. Dead Shores
- 35. Flying Shores
- 36. Scaffold type shoring • Scaffolding was first designed to support loads imposed by workers • Often used as support for formwork • Provides rapid utilisation for formwork support
- 37. Underpinning
- 38. What is underpinning? • Strengthening and stabilising the foundation of an existing building • Installation of temporary or permanent support • Provides additional depth or increase bearing capacity
- 39. When do we need underpinning? • Construction of a new building adjacent to the old one • Settlement of an existing building • Change in how a structure is used • Need to add a basement below an existing building
- 40. Temporary support with maintenance jacking • Light structures may be supported with timber or concrete mats • If settlement occurs, mechanical or hydraulic jacks keep the structure level
- 41. Bracket pile underpinning • Steel bracket piles driven adjacent to the structure • Load is transferred from the structure into the pile through a steel bracket • Backfilled with lean sand cement mix
- 42. Minipiles • Minipiles inserted through the existing foundation • Generally do not require temporary support of the building
- 43. New foundation wall and footing constructed underneath the existing foundation • • • The area is excavated The new footing is constructed The excavated area is backfilled
- 44. Support during underpinning • • Digging trenches at intervals This leaves most of the foundation supported by the soil
- 45. Support during underpinning • • • Using needle beams Beams are threaded through holes cut in the wall Entire wall can be exposed at once