Study On The Reliability And Behaviour Of Reinforcing Bond In Reinforced Masonry

The code for design of masonry structure (GBJ3-88) has been revised entirely since 1998. Based on theoretical analysis and test results, the technology relating to reinforced masonry structure has been introduced. Compared with reinforced concrete structure, reinforced masonry structure is more complicated. According to the feedback opinions and the provisions presented in the Code for Design of Masonry Structures (Enquiry Document), the bar anchorage and lap length are not only conservative and arbitrary, but also lacking in test data. Therefore, experiments on the bar anchorage and lap length in the bed joints, grout cells and bond beam was carried out. Finally, the reasonable suggestions are presented in this paper. Main research results as follow:1. Tests and research on anchorage length and lap length of reinforced bond According to the specification of Code for Design of Masonry Structure (Enquiry Document), more than 76 specimens were tested. Which contains 24 specimens of bed joints, 32 specimens of grout cells and 20 specimens of bond beams. Based on theoretical analysis and test results, suggestions for the bar anchorage and lap length in reinforced masonry are presented as follows:(1) For ungrouted masonry, joint reinforcement shall be fully embedded in mortar. The anchorage length of the joint reinforcement shall be 50d and have a hook with a 90-degree bent, plus an extension of not less than 15d or 200mm. The bar lap length shall be 55 d.(2) In bond beams, the bar anchorage length shall be 30d and have a hook with a 90-degree bent, plus an extension of not less than \5d or 200mm. The bar lap length shall be 35d.(3) In grouted cells, the bar anchorage length shall be 30d for HRB335, 35d for HRB400 and RRB400. The anchorage length shall be 300mm and have a hook with a 90-degree bent, plus an extension of not less than 150mm for smaller diameter cold-rolled bar.(4) The bar lap length shall be 35d for contact lap, 40d for noncontact lap and the bar space should not exceed 75mm.2. Tests and Research on Reinforced Bond in Mortar The test results of 30 pull-out specimens are presented as follow:(1) The P-S curve of the pull-out test indicates that the loading process of the anchor bar in mortar can be divided into five phases generally: slight slip phase,internal crack slip phase, crack phase, falling phase and residual phase.(2) Anchorage strength is directly proportional to mortar tensile strength, and varies inversely to the relative anchorage length.(3) This paper presents an analysis of the influence of mortar strength, anchorage length and bar diameter on anchorage behavior, establishes Ï„-s characteristic curve and proposes an anchorage strength calculating formula by means of regressive equation. Statistical results of test data also indicate that mortar strength has no obvious effects on relative characteristic slip value.3. Tests and Research on Reinforced Bond in GroutBased on test results of 36 cubic specimens and 36 block specimens of grout, load-slip curves and the corresponding bonding stress-slip curves are gained.(1) According to the development of the curves, the process of the load-slip curve is divided into five phases: slight slip phase, internal crack slip phase, crack failure phase, falling phase and residual phase. By the analysis of the influence of grout compression strength, anchorage length and bar diameter on anchorage behavior, the formulas of the characteristic strength value and characteristic slip value are attained by means of regressive equation. Consequently, the basic bond stress-slip relations are established.(2) Based on the test with strain gauge stuck on the internal groove of the bar, the stress distribution along the anchorage length is studied. According to the bond stress vs. anchorage length curve, the distribution function of the bond stress along the anchorage length is presented.(3) Based on the interlock action test, the development of the internal crack and the whole process of bond-anchorage failure of the specimens are observed. Meanwhile,...