Staged Construction Analysis of Steel Bracing Retrofit in Reinforced Concrete Structure

Changes in building functions and regulations are the reasons for strengthening of existing structures. This change resulted in an increase in planned earthquake load and increased structural detail requirements. In theory, a building structure that is designed using the old SNI will experience an over stressed stress if it receives a plan earthquake load according to the new SNI. So, what strengthening methods can be used to prevent this from happening?

Addition of steel bracing to the frame structure is one method to increase the strength and rigidity of the existing structural system. This retrofit requires a short working time and does not have a significant influence on the weight of the structure and its installation can be done on the outside (exterior) of the building, so it does not interfere with activities within the structure. At the time the steel bracing was added, the structure is already in a deformed state. So the analysis must take into account the deformation that has occurred. One analytical method that can be used is a phased construction analysis.

Stage construction analysis is part of the nonlinear static analysis which analyzes structures in several phase levels / stages (Analysis Reference Manual SAP2000, 2002). The basic idea of ​​this analysis is that at the initial stage the initial conditions of the structure are zero. All elements are not yet loaded and deflection has not occurred. For the next analysis phase, it is a continuation of the nonlinear analysis in the previous stage. The purpose of this statement is that the internal forces, deflections and cross-section cracks in the previous stage are included in the next stage analysis. In a stage construction analysis, the results of the final analysis will be used as a reference.

In the application of analytical methods, especially in structural retrofit, the methods that was often used is conventional, in which the bracing retrofit is analyzed together with the loads, without taking into account the condition of the existing building which has been deformed due to its own weight and service load while the building is standing (before being strengthened). Therefore, in structural analysis with retrofit, it is better to use a stage construction analysis, because it gives results that are more in accordance with field conditions so that the retrofit applied to the building functions as it should.