Case study: Evaluation of a two-level residence structural plan (stilt house with open space on the first floor) and compliance recommendations for earthquake resistance in Puerto Rico using ACI318-14 code

Abstract

The construction of two-level residences on columns in Puerto Rico is quite common. This type of structure is built for the purpose of having an open space on the first floor (ground level) while the main residence is built on the second level. In this case study, an original design was evaluated against existing codes to bring it to compliance. Recommendations are presented with the objective of ensuring that the structure is adequately designed as an earthquake-resistant moment frame according to code ACI318-14. The first analysis considers the properties of materials, live loads, dead loads, and seismic loads based on the structure's own weight (applied at a distance equivalent to 5% of the centroid). It also considers the P Delta effects. All these loads are factored in and combined in order to decide which one is the worst-case scenario. The capacity of each element should be verified with the maximum load obtained from the analysis; if not compliant, the structure must be redesigned. When the cross section of an element changes in size, components, or material property, it is necessary to redo the analysis. This iterative process should be carried over until the sections obtained have a capacity (multiplied by a reduction factor) greater than the maximum demand. Furthermore, it is necessary to comply with important aspects such as the minimum spacing of transverse steel (shear), minimum dimensions of elements, maximum and minimum and maximum amounts of longitudinal steel (flexure), location of development lengths and splices, and verification of strong column-weak beam criteria (MnColumns>1.2MnBeams), among others. Key terms ⎯ earthquake resistant, stilt houses, strong column-weak beam, two-level houses