Repairable Precast Buildings

Sponsor:  

South Dakota State University

Project Funds:  $10,000

Year:  2015-2018

Personnel:  

PI:  Mostafa Tazarv, PhD, PE

Graduate Research Assistant:  Abdullah Boudaqa (PhD) and Ishtiaque Tuhin (MS)

Industry Collaborators/Donors:  Headed Reinforcement Corp.,  Saes Smart Materials.

Project Summary:

 A new moment-resisting precast connection has been developed through experimental and analytical studies to accelerate construction of bridges and buildings, to improve their seismic performance, and to quickly repair them through replacement of exposed reinforcement.  The new precast joint detailing incorporates (1) detachable external reinforcing steel bars restrained against buckling, which is referred to as buckling restrained reinforcement (BRR), to develop plastic bending moments, (2) a steel pipe connecting the precast members through a pin connection to resist plastic shear forces, and (3) detachable mechanical bar splices to assemble and disassemble BRR at any time specifically after server event as a quick repair method.  

Feasibility and performance of a new type of BRR that can be used as detachable external reinforcing steel bars, were experimentally investigated.  Furthermore, a simple design method for BRR with or without a section modification (e.g. dog-bone) was presented to further help engineers with the design of external reinforcement and energy dissipaters.  

The seismic performance of the proposed repairable precast connections was investigated through cyclic testing of four half-scale beam-column specimens detailed based on a nine-story building designed for Los Angeles, which is a high seismic region.  A reference cast-in-place beam-column specimen was also included for comparison.  The test results showed that the repairable precast connections can withstand more than fourteen times the design level earthquake with insignificant damage and ability to be repaired afterward.

Furthermore, a comprehensive analytical study including pushover and nonlinear response history analyses was performed to investigate the seismic performance of three-, six-, and nine-story repairable precast and cast-in-place (CIP) buildings, and repairable precast bridge columns.  It was found that the stiffness of the proposed precast system is 60% of conventional cast-in-place structures but the displacement capacity of the proposed precast structures can be four times higher than that in the conventional structures.  The increase in the displacement demands of the precast systems due to lower initial stiffness is usually within the design limits and there is no need to increase the member sizes.  

Based on the construction, and experimental and analytical studies, it can be concluded that the proposed precast connection detailing is expected to improve the seismic performance of bridges and buildings, to expedite the construction, and to eliminate the need of structure total replacement after severe earthquakes since the repair is done by replacement of exposed bars.  

Project Work Plan:

Task 1:  Develop a new precast connection detailing with exposed reinforcement.

Task 2:  Test buckling restrained reinforcement (BRR) and develop a simple design equation for BRR.

Task 3:  Test a half-scale reference cast-in-place beam-column joint. 

Task 4:  Test precast beam-column joints, repair them by replacing exposed reinforcement, then retest them. 

Task 5:  Perform analytical studies to investigate the seismic performance of buildings and bridges incorporating the new detailing. 

Publications:

1.  Tazarv, M., Boudaqa, A., and Tuhin, I.A. (2020). “Repairable Precast Moment-Resisting Buildings: Part I – Experimental Investigations,” ACI Structural Journal, Vol. 117, No. 6, 147-160 pp. (Link).

2. Tazarv, M., and Boudaqa, A. (2020). “Repairable Precast Moment-Resisting Buildings: Part II – Analytical Investigations,” ACI Structural Journal, Vol. 117, No. 6, 161-170 pp. (Link).

3. Tazarv, M. and Boudaqa, A. “Repairable Precast Moment-Resisting Buildings”, US Patent No. US20190078315A1 (Link).

4. Boudaqa, A., Tazarv, M., and Tuhin, I. (2017). “Ductility without Confinement - A New Design and Construction Approach for RC Bridge Columns,” International Journal of Bridge Engineering, Special Issue, pp. 53-77 (Link).

5. Boudaqa, A. (2018). "Repairable Precast Buildings and Bridges", PhD Dissertations, South Dakota State University, 278 pp., (Link). 

6. Tuhin, I.A. (2016). "Application of New Materials and Innovative Detailing for Reinforced Concrete Structures" MS Thesis, South Dakota State University, 181 pp., (Link).

Slow-Cyclic Test Results:

First, the precast specimen with steel BRR was tested up to the displacement in which the reference cast-in-place specimen failed by bar fracture.  Subsequently, the precast specimen was repaired by simply replacing the exposed bars.  Shape memory alloy (SMA) BRR were used in the repaired joint and was retested to failure.  The damage of the precast members was insignificant even at 14 times the design level earthquake.