Implications of Experiments on the Seismic Behavior of Gravity Load Designed RC Beam-to-Column Connections

Abstract

This paper summarizes recent experimental research at Cornell University conducted on the behavior of gravity load designed reinforced concrete building frame components subjected to reversing cyclic loads (simulated seismic effects). Reinforced concrete framing systems, designed primarily for gravity loads, with little or no attention given to lateral load effects, are typically characterized by non-ductile reinforcing details in the joint regions and in the members. The seismic response of connection regions for gravity load design (GLD) frames has received relatively little attention in earlier studies, thus making it difficult to reliably evaluate GLD frames and to properly plan repair or retrofit strategies. Thirty-four full scale bare interior and exterior beam-to-column joints have been tested under reversed cyclic bending to identify the different damage mechanisms and to study the effect of critical details on strength and deformations. The discussion of test results focuses on the definition of joint shear strength factors for GLD frames to complement those provided by ACI-ASCE Committee 352 for frames designed with better details.

Experimental and Numerical Validation of Selective Weakening Retrofit for Existing Non-Ductile R.C. Frames

“…1 Failure point defined as attained peak force is less than 80% of previous peak force; 2 Maximum column moment attained in the test. 3 Calculated maximum column moment based on heirarchy of strength of b-c joint elements 4 No failure (based on the definition) achieved.…”

“…It is widely recognised that poorly detailed nonductile reinforced concrete (RC) moment-resisting frames pose significant risks to urban population in seismic zones. Research on the seismic performance of pre1970s (prior to modern seismic codes) or non-ductile, mostly gravity-only designed, rc frame at sub-assemblies levels [3,4] as well as at a large-scale frames level [5,6] have shown the importance of robust and strong b-c connections in collapse prevention. The poor joint behaviour of older construction can be attributed to: the inadequate shear reinforcement in joint region, the poor bond properties of plain round bars reinforcement, the deficient anchorage details into the joint region and the lack of capacity design consideration.…”

Multi-level seismic rehabilitation of existing frame systems and subassemblies using FRP composites

“…Extensive experimental-analytical investigations on the seismic performance of existing reinforced concrete frame buildings, designed for gravity loads only, as typically found in most seismic-prone countries before the introduction of adequate seismic design code provisions in the 1970's, confirmed the expected inherent weaknesses of these systems (Aycardi et al, 1994;Beres et al, 1996, Hakuto et al, 2000, Park, 2002Pampanin et al, 2002;Bing et al, 2002;Calvi et al, 2002a,b). As a consequence of poor reinforcement detailing, lack of transverse reinforcement in the joint region as well as absence of any capacity design principles, brittle failure mechanisms were observed.…”

Seismic Retrofit of Defective RC Beam-Column Joints

“…Scarce information is available on connection repair and strengthening' ' (p. 20). In the past four decades, multiple studies were performed to assess the seismic behavior of the existing reinforced concrete beam-column joints designed in accordance with different codes of various countries [12][13][14][15][16][17]. In the previous two decades, the seismic retrofitting of imperfect RC beam-column joints has been given substantial attention and multiple techniques have been proposed to seismically retrofit the reinforced concrete beam-column joints [18][19][20][21][22][23][24][25].…”