Study Of Repaired And Strengthened RC Beams Using Different Jacketing Techniques

Abstract

Strengthening of Reinforced Concrete (RC) beams is required due to design errors, de cient concrete production, bad execution processes, damage due to earthquake, an accident, such as collisions, re, explosions and situations involving changes in the functionality of the structure etc. It is known that many buildings designed based on older codes may be susceptible to serious damage during such accidents. Older buildings have been structurally designed for much lower load carrying capacity as compared to that of buildings which are designed today. Structural rehabilitation brings a structure or a structural member to a speci ed safety and performance level. Depending on state of a structure or a structural member, rehabilitation can be di- vided into two categories: Repair and Strengthening. Repair is the rehabilitation of a damaged structure or a structural member, on the other hand strengthening is up- grading an undamaged structure or the member. Various methods for strengthening of RC beams are being employed in practice. Jacketing has been considered as one of the important methods for strengthening and repairing of RC beams. Jacketing is done by enlarging the existing cross section with a new layer of concrete that is reinforced with both longitudinal and transverse reinforcement. Total eighteen RC beams of size 150mm x 300mm x 2.1m span have been cast. Eight beams are considered for strengthening. Other eight beams are considered for re- pairs and strengthening. Remaining two beams are considered as control beams. Four beams from each strengthened and repaired and strengthened category have been kept as-cast with smooth surface. Surface of remaining four beams from each strengthened and repaired and strengthened category has been chipped for about 10- 15mm from all the sides. Eight strengthened beams have been jacketed using additional reinforcement for 60mm thickness all-round. For eight repaired and strengthened beams, all beams are loaded up to its failure and repaired by means of grouting. For checking e ec- tiveness of grouting for lling up of cracks, Ultrasonic pulse velocity test is conducted on all grouted beams. After grouting, increment in pulse velocity of grouted beams has been observed as compared to non-grouted. The jacketing is executed for all beams after grouting. Jacketed beam cross-section is considered as 270mm x 420mm. Four di erent methods have been employed for jacketing of RC beams in the present investigation. These methods include use of dowel connectors and micro-concrete, bonding agent and micro-concrete, combined use of dowel connectors, bonding agent and micro-concrete and without dowel connectors, bonding agent and use of only micro-concrete. All four methods have been employed for jacketing of the beams with the smooth as well as the chipped surface. RC beams have been tested with two point loading. Comparative performance of strengthened and repaired and strengthened beams has been evaluated. Failure load, displacement at mid span and below the point load, strain variation in concrete at dif- ferent locations, failure modes and crack pattern has been evaluated for all the beams. Most e ective techniques of jacketing for strengthening of RC beams with di erent surfaces has been evaluated. Comparative assessment has been done on the e ective- ness of each type of method of jacketing RC beams with smooth and chipped surfaces. For smooth surface strengthened beams and repaired and strengthened beams, higher load caring capacity, higher displacement and higher strain has been observed for beam with combined use of dowel connectors, bonding agent and micro-concrete. For smooth surface repaired beams and strengthened and strengthened beams, higher ex- perimental load has been observed for same beam as compared to that for analytical load. For chipped surface strengthened beams and repaired and strengthened beams, higher load caring capacity, higher displacement and higher strain has been observed for beam with only micro-concrete without dowel connectors, bonding agent. For smooth surface repaired beams and strengthened and strengthened beams, higher experimen- tal load has been observed for same beam as compared to that for analytical load. For all strengthened and repaired and strengthened beams load carrying capacity evaluated is within range of 1.69 % to 16 %. It has been observed that when re- quirement of change in utility of structure occurs, strengthening by jacketing is more suitable. For fully damaged structure, repairing by grouting and strengthening by jacketing is more suitable. For smooth surface beam jacketing method of combined use of dowel connectors and bonding agent with micro-concrete is more advantageous in term of bond between old to new concrete. For chipped surface beam jacketing method of using only micro-concrete without dowel connectors and bonding agent gives good bond between old to new concrete.