Lap Strength Research Articles

Lap Strength of Headed Steel Reinforcements with Confinement

In this research, the experimental works were conducted to study the lap strength of the headed reinforcements with confinement provided by stirrups or tie-down bars. Five lap splice specimens were tested. Wide beam specimens were fabricated with a lap splice at mid-span. They were loaded in flexure, placing the lap splice in tension. The variables in this study were: confinement details (stirrups, tie-down bars with stirrups) and lap length (10, 14 times the diameter of reinforcement). Specimens were instrumented to measure the load on the specimen, strain along the reinforcements with in the lap zone, and mid-span deflection. The cracking behavior was also observed and recorded. The following conclusions were drawn from the test results in this study; 1) The initial crack of the specimens lapped developed at the heads of reinforcements. The specimens failed by the crack with the struts acting between the opposing heads of lapped reinforcements. 2) Bond stress and confinement details contributed to increase strength and deformation. 3) CCD method evaluated the maximum strength as 4.95∼6.87 times the test maximum strength. The ratios of the test maximum strength and the maximum strength assumed by ACI 318-08 for headed deformed bars were 1.38∼2.01.

Research of silver plating nano-graphite filled conductive adhesive

In this paper, silver plating nano-graphite (Ag plating nano-G) was developed by electroless plating method using nano-graphite prepared from expanded graphite. The silver plating nano-graphite filled conductive adhesive prepared was composed of 66 wt% of epoxy resin E-51, 20 wt% of Ag plating nano-graphite as conductive filler, 9 wt% of triethanolamine as curing agent and 5 wt% of other additives. It took 180 min for the adhesive to be cured completely at 120 °C. The electrically conductive adhesives exhibited two percolation threshold values which were 7 wt% and 17 wt%, respectively. The electrical resistivity of the conductive adhesive decreased to 1.50 × 10 −3 Ω cm and the tensile lap strength remained at a high level (about 13.2 MPa) when the content of the conductive filler was 20 wt%. TGA indicated that the conductive adhesive exhibited good thermal stability.

The Durability of Adhesively-bonded Ti-6Al-4V

The durability of chromic acid-anodized Ti-6Al-4V alloy, adhesively-bonded with FM-5 supported polyimide adhesive has been studied. The performance tests compared titanium samples that had been thermally treated and bonded, and samples that were bonded and thermally treated. Following the thermal treatment, the durability was examined (1) by immersing wedge-type specimens in boiling water and measuring the crack growth and (2) by measuring the lap shear strength for single lap specimens. In the wedge tests, failure occurs within the adhesive for specimens treated at temperatures below 371°C for less than one hour. For treatments at higher temperatures and for longer periods of time, failure occurs within the anodic oxide. From the lap shear tests, the principal finding is that the lap strength decreases with increasing treatment time at constant temperature and with increasing temperature at a fixed time. For the lap specimens, failure occurs to a greater extent within the oxide as the treatment time and temperature increase. Surface analysis results indicate the formation of an aluminum fluoride species. It is reasoned that the formation of fluorine-containing materials weakens the oxide and promotes failure within the anodic oxide.

North American approach to the design of continuous Z- and C- purlins for gravity loading with experimental verification

The design of cold-formed, through fastened, roof purlins requires a significant number of assumptions. The usual North American practice is to make the following major assumptions: constrained bending, full continuity through the lapped section, and a lap strength equal to the sum of individual purlin strengths. To verify these assumptions, test results of multiple span purlin systems were gathered from 10 laboratories. Of the 45 test results reported, 24 were found to be sufficiently documented for complete evaluation. Comparison of the test results and analysis/design procedures using the above assumptions and AISI specification provisions showed that the assumptions are valid.

DESIGN OF CONCRETE STRUCTURES USING FUSION-BONDED EPOXY-COATED REINFORCEMENT.

The paper reviews structural aspects of fusion-bonded epoxy- coated reinforcement (FBECR) which may differ from that of non- coated reinforcement, proposes guidelines for structural design using FBECR in respect of those differences, and presents a rationale for these proposals. The study shows that coating of reinforcement to BS 7295 will not adversely affect mechanical properties, fatigue endurance or bendability of reinforcement. Bond behaviour is affected, however. A review of data demonstrates that anchorage and lap strength of reinforcement is reduced by an FBE coating where concrete cover is less than three times bar diameter. The paper concludes with proposals for design detailing with FBECR, and for changes to methods for bond testing; and it identifies areas in which further data are required. Conclusions from the study raise questions about the value of the BS 4449 test specification when applied to coated bond reinforcement.

An analysis of the ultimate strength of lapped joints of compression reinforcement

Synopsis Bond failure of ribbed reinforcing bars generally takes place by splitting of the surrounding concrete cover, unless heavy confining reinforcement is present. The bond action of the bars must therefore exert a radial bursting force on the concrete cover, and so the ultimate strength of a lapped joint may be calculated by equating the bursting force produced by bond to the ultimate confining force on the lapped bars provided by the member. In this paper, expressions are derived for the relationship between the stress developed in a lapped bar and the resultant bursting force and they show that this depends mainly upon the strength of the concrete in the member and the deformation characteristics of the bar. The contribution made by bearing of the ends of lapped bars to the ultimate strength of compression laps is also evaluated. Values of lap strength calculated from the analysis are shown to be in good agreement with results obtained from tests on lapped joints in reinforced concrete columns.