Seismic performance of pre 1970s non-ductile reinforced concrete waffle slab frame structures constructed with plain round reinforcing steel.
Thesis DisciplineCivil Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis investigates the seismic performance of components of a typical pre 1970's New Zealand non-ductile reinforced concrete waffle slab frame structure constructed with plain round reinforcing steel. The experimental program tests the top and bottom sections of a typical concrete column, and a two-bay waffle floor slab sub-assemblage. The specimen of the scaled bottom section of the typical column is an octagonal section with a circular reinforcing steel arrangement on a pitch circle diameter of 41 Omm. The reinforcing steel is lapped at the base with a lap length of 45db. The analysis and results indicate a lap-splice failure mechanism with pinching of the hysteresis loops after the nominal flexural capacity of the specimen is reached. The section has an effective moment of inertia of O. l 6Ig and a yield drift, 8y of 0.62%. It is possible from the new theory developed to predict whether a lap-splice failure mechanism will form and at what stage strength degradation begins. Hysteretic · modelling of the experimental results is possible with the proposed hysteresis rule. The specimen of the scaled top section of the typical column is an octagonal section with a 215mm high column capital. The reinforcing steel arrangement is circular on a pitch circle diameter of 41 Omm with additional reinforcement at 45 degrees in the column capital. The analysis and results indicate a flexural failure mechanism with pinching of the hysteresis loops due to slip of the reinforcement. The section has an effective moment of inertia of 0.19Ig and a yield drift, 8y of 0.65%. Hysteretic modelling of the experimental results is possible with currently available hysteresis rules. The scaled two-bay waffle floor slab sub-assemblage supported by three central columns is tested to determine the critical failure mechanism. Scaling symmetry and elongation allowances are incorporated into the design of the testing setup. The results match the structural assessment predictions of a unidirectional flexural yield line failure mechanism. The effective moment of inertia of the floor slab is 0.43Ig and the full flexural strength is reached at an interstorey drift of 1.0%. The bay elongation characteristics of the specimen are matched by the theory for elongation of unidirectional hinges. Elements of an assessment methodology for reinforced concrete structures are discussed and the outcomes of such an assessment related to damage state indices for both pre and post earthquake assessments. Specific examples from the experimental program are used to illustrate the damage state outcomes of this testing.