|M.Sc Student||Jaber Ghali|
|Subject||Quantification of the Structural Properties of|
Unreinforced Plum Concrete Walls
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Avraham Dancygier|
|Dr. Rami Eid|
|Full Thesis text - in Hebrew|
Small to medium buildings of up to 4-stories height were constructed in Israel more than five decades ago with low-performance concrete. This type of concrete is characterized by low compressive strength (~10 MPa or less) and/or by relatively large aggregates (up to maximum size of ~300 mm) as part of its ingredients and it is known as 'plum concrete' (PC) and in Israel - as "DEBESH concrete". PC was used in exterior unreinforced walls, and in many cases, also in interior partitions, which were designed and constructed to carry gravity loads. These old structures were not designed to withstand earthquake loading. Yet, PC walls have relatively large dimensions and hence - stiffness, and therefore they are likely to attract substantial proportion of the lateral seismic loads during future earthquakes. Strengthening of existing buildings, made of PC and which are not intended to be demolished, is thus crucial. However, design of PC walls strengthening, based on current design codes' provisions, cannot be carried out directly, because of their non-standard material properties.
This experimental research aimed at providing structural engineers, who consider seismic retrofit of buildings with plum concrete walls, with empirical assessment of their concrete material properties, namely, the elastic modulus, tensile and shear strengths.
The experimental study includes specimens that were taken from authentic samples that had been extracted from existing PC walls and brought to the laboratory. First, the relations between the concrete uniaxial compressive strength and its tensile strength and elastic modulus were determined in a series of tests. Then, relevant structural tests were performed. A non-standard diagonal compression test setup, which is commonly used to determine the shear strength of masonry walls, has been adopted for testing of PC specimens. Such adoption was considered pertinent because of the similar structural characteristic of masonry and of PC with its large stones. An additional set of control specimens, made of low-class, yet standard concrete, was also tested with a two-fold purpose: one was to measure their properties, with which the authentic specimens can be compared, and the other was to verify these properties against code formulas. Results of the diagonal compression tests showed that under the combined action of horizontal and gravity loads, squat walls would fail in diagonal tension, which is controlled by the concrete tensile strength (and not by its flexural shear capacity).
To examine and evaluate the shear capacity of unreinforced plum concrete slender walls, authentic beam specimens, as well as specimens prepared at the laboratory were tested in a three-point-bending test setup. These beam specimens' flexural resistance was strengthened by gluing FRP sheets to their bottom surface, thus leading to their shear mode of failure.
The results of the above-described tests showed that the existing relations, used to evaluate elastic modulus and tensile strength of standard concrete, based on its uniaxial compressive strength, are not suitable for plum concrete and alternative relations have been proposed.
Findings of this study provide valuable data and useful information for the assessment of the resistance and capacity of existing plum concrete shear walls.