Design of joints for laterally loaded UHPC columns

Srinivas Murthy, Rakesh
Major Professor
Sri Sritharan
Committee Member
Journal Title
Journal ISSN
Volume Title
Research Projects
Organizational Units
Journal Issue
Civil, Construction, and Environmental Engineering

This study focuses on the use of Ultra-High Performance Concrete (UHPC) on seismic applications. As part of this effort, UHPC members have been tested for the first time under non-emulative connections for resisting seismic type lateral loads. Due to the limited compression strain of UHPC, identifying a suitable soft interface material at the member end was the main objective in order to accommodate large compression strain demand so that the UHPC members can be subjected to large lateral displacements.

Three precast unbounded post-tensioned UHPC columns were experimentally and analytically investigated using three different interface materials. They were Hydrostone, steel fiber grout and glass fiber epoxy pad along with easily replaceable external steel angles as energy dissipaters. Through this investigation, it was intended to establish a precast UHPC column connection with replaceable external energy dissipater and adequately deformable member end interface as these features enable the UHPC columns to be used in seismic applications. Before testing, a finite element model was developed to predict the lateral load behavior of the test columns, using all known UHPC properties and assumed interface material properties. To study the influence of the pad on the system, the UHPC columns were first tested for few cycles only with the pad. In addition to repeating these cycles, they were tested under large lateral displacements after the external energy dissipaters had been added. As the tests were conducted, samples from the interface materials were collected and tested separately for obtaining compressive stress-strain envelopes, which were later used in the finite element model to improve the analysis results.

Based on the research results, it was found that the Glass fiber epoxy performed better than other interface materials and the analytically calculated load versus displacement responses closely matched with the responses of all the experimental results. It was also found from the analysis that use of hollow UHPC columns may be adequate as this would lead to cost-effective design.