Tensile behavior of concrete and mortar under direct impact tensile load

Structures are often subjected to impact loadings during their lifetime. Most structural specifications including the special provisions for seismic design in the current ACI building codes, have been developed on the basis of quasi-static assumptions. Cement composites are strain rate sensitive materials therefore, their properties determined under quasi-static condition should not be used to predict their performance under high strain rates.;The objectives of this investigation are: (1) to develop a standard test set-up for direct tensile testing of cementitious composites; (2) to study the tensile behavior of mortar and concrete under direct impact tensile load; (3) to develop a simplified formula to predict the behavior of mortar and concrete under direct tensile impact loading.;A unique specimen was developed for this study based on a coaxial cylindrical design and is used to investigate the direct tensile behavior of cementitious composites. A specially instrumented drop weight testing apparatus was used for this study.;Wave propagation analysis was carried out on the proposed test specimen using the ANSYS finite element program to verify the uniform stress distribution across the specimen thickness. Strain rates of 0.03 to 0.97 1/Sec were achieved during these experiments by varying the instrumented drop-hammer height and the rubber-pad thickness at the contact zone between the drop-hammer and the specimen.;It was found that tensile properties of mortar and concrete were strain rate sensitive. The peak tensile loads and strains under direct impact tensile load were 1.9 and 1.7 times those obtained under static loading respectively. By increasing the strain rate, the stress-strain curve becomes less non-linear. Dynamic energy absorption to failure was found to be 3.9 times the energy absorbed under static loads. Cracking pattern was found to be one of the major differences for the observed strain rate effects in concrete composites.;A model is proposed based on the constitutive law to evaluate the response of the test specimen subjected to an impact load. The model is capable of predicting the rate sensitivity behavior of mortar and concrete under impact loading.