EXPERIMENTAL AND THEORETICAL STUDY OF MOMENT REDISTRIBUTION AT SLAB-COLUMN CONNECTIONS

Abstract

From the revision of literature, it was found that no few work has been done to study the moment redistribution occurring at slab-column connection after cracking of concrete, yielding of tension reinforcement and at failure with different column dimension / span ratios and different reinforcement layouts. No provision has been given in Egyptian code of practice. Various international codes of design limit the amount of moment redistribution to avoid brittle failure due to concrete crushing and to insure satisfactory behavior at service loads. In ACI 318-11, a limited moment redistribution of the end span (at slab-column connection) and mid-span factored bending moments is permitted. The redistribution of moments based on elastic theory has to been less than 20 % while Euro code 2 permits to 30 % . Hence, an extensive investigations from experimental results and theoretical study was carried out to study the amount of moment redistribution at different load levels for different mentioned parameters. 118 7.2. Conclusions As a result of these experimental and theoretical investigations, the following main conclusions could be drawn: 1- Deflection decreased as column dimension / span ratio increased at the same load level. The ultimate load capacity increased by about 50 % when column dimension / span ratio increased from 0.06 to 0.11. 2- Bottom steel reinforcement at slab edge influenced significantly the ultimate load capacity which increased by about 30 % when the ratio of bottom to top steel reinforcement area increased from 0.64 to 1.44. No significant increase of ultimate load capacity when the ratio of top to bottom steel reinforcement area increased to the same ratio. 3- At failure, the total static moment absorbed by the slab-column system increased as the column dimension / span ratio increased. The summation of moments at column face and at slab edge increased for larger column dimension.. 4- Flat slab shows significant moment redistribution at slab-column connections between the uncracked state and maximum load. The moment redistribution is not substantially influenced by the column dimension nor the reinforcement layouts after cracking, until first yielding. Where the moment redistribution is constant value 25 %. 5- A comparison between the theoretical results and the allowable limits of the codes for moment redistribution showed reasonable agreement at serviceability limit state. 119