Archive for the ‘Exterior Detailing’ Category
Exterior Detailing
Precast columns are effective in cutting down the construction time at the project site because of no need of positioning and curing of concrete to build substructures. Precast column structural details requires careful investigation of the strength and ductility performance and dynamic behavior under various loads and conditions. For a right design approach, a detailed study is required of joints, PC cables, segments, bar bending, dynamic loads and material availability at the site. Sometimes a series of repeated loading tests and analysis were made to produce seismic guidelines for column design.
Precast column segments efficiently use the mixture of high strength materials like concrete and steel and are fabricated at factory to easily achieve better quality and performance. In this way precast columns enhances the constructionability at project site and curtail the construction time. These segments are piled up at the site to bond them as a column. PC cables are used not for tensioning but to ensure strong joint connections between the column members. After staking all members, longitudinal steel rebars are placed into the segment sheathes to inhibit buckling of the columns.
The precast column segments contain outside concrete housing one or more inner steel shells. Inner steel shells of the members are connected by steel bolts. After piling up all column members perpendicular tensioning is enforced by inner PC cables. Shear keys are provided at the steel joints between segments along with concrete mortar which is placed between the members exterior to concrete. Hence axial forces generated by live and dead loads is supported by inner steel shell but the seismic force is carried by exterior concrete and steel bolts. Steel joints and shear key carry typically carries the shear force applied to the column.
PC cables, steel bolts and shells act as longitudinal steel. The bolts are intended to be firstly conceded when the buckling is going beyond the elastic limit and then the steel shells are not likely to be damaged. It is essential to that the yielded bolts can be easily replaced after seismic disturbances and then the steel columns can be certainly recovered to their primary state.