Akhrawat Lenwari

SED Method of Measuring Yield Strength of Adhesives and Other Materials

The strain energy density (SED) method of determining the yield strength of adhesives and other materials that is based on the fundamental principles of mechanics is described in this paper. The results from two sets of tests are reported. In the first set, the yield strength of multiple specimens made of the adhesive FM 300K was determined in the dry/cold, moderate, and humid/hot environments; the strain rates were 10−2/s, 10−4/s, and 10−6/s. In the second set, single specimens of five other adhesives were tested in the dry/cold and humid/hot environments; the strain rate was 10−4/s. Fifty-three out of the 60 specimens have yield strengths calculated with the SED method that are equal to or lower than the values obtained with the 0.2% offset method suggested in the ASTM specifications. The SED method is most valuable when the stress-strain curve of the material exhibits a gradual transition from elastic to the inelastic behavior typical of polymers, aluminum, and some very high strength steels. To ensure the safety of bonded structures, the yield strength of adhesives should be determined with the SED method, which is based on the fundamental principles of mechanics, instead of on an arbitrary estimate of strain offset. Although applied in this paper to stress-strain curves of adhesives, the SED method may also discern the onset of yielding and instability in columns and beams. To ensure that the yield strength of adhesives for bonding load-bearing structures is not systematically overestimated, the authors recommend using the SED method in lieu of the 0.2% offset method.

A study of the fabrication of M4 military bridge aluminium floor joists using domestic materials

The objective of this research is to study a fabrication of aluminum floor joists using domestic materials. The study includes the review of aluminum alloy available in Thailand. Different types of domestic aluminum alloys were tested for the ability to form to shape and weldability. The result shows that cold-forming and built-up using screws are capable to fabricate the M4 military bridge floor joists. However, fabrication by welding method is not suitable. Therefore, the built-up shape connected with screws was chosen to fabricate M4 military bridge floor joist. The fabricated floor joist was designed according to British Standard (BS.8118 - structural use of aluminum) and tested to verify its strength and stiffness. The results are presented within this paper.

Thermal Analysis for Peak Temperature Distribution in Reinforced Concrete Beams after Exposure to ASTM E119 Standard Fire

To assess the post-fire or residual strength of fire-damaged reinforced concrete (RC) members, the most detrimental or peak temperature distribution within the members should be perceived. For RC beams, the residual flexural response is strongly influenced by the peak temperature experienced by the steel reinforcements. This paper presents a simplified two-dimensional (2D) nonlinear transient thermal analysis for the peak temperature distribution in RC beams using the finite element method. In the analysis, the thermal loading for heating was the ASTM E119 standard fire. After heating, a linear decrease in temperature was assumed for cooling. Three-sided fire exposure was assumed for rectangular RC beams. The analysis was used to investigate the effects of the heating period (1–4 h), cooling period (1–4 h), concrete cover thickness (30–50 mm) and aggregate type (carbonate or siliceous aggregates) on the peak steel temperature and delayed time (time to attain the peak temperature after heating). The numerical results showed that the temperature inside the beam section continues to rise after heating. The increases in steel temperature after heating and delayed time are influenced by the heating period, cooling period, location of steel reinforcement, and aggregate type. Such increase is significant for the beam with a thick concrete covering subjected to a short heating period followed by a long cooling period. At the longest (4 h) cooling and shortest (1 h) heating periods, the increases in steel temperature after heating in both carbonate and siliceous concrete beams are approximately 35, 50 and 75% for concrete cover thicknesses of 30, 40, and 50 mm, respectively. The carbonate concrete beams are more vulnerable to fire damage than siliceous ones when subjected to long heating and cooling periods.

Field Investigation on Slab-on-Girder Steel Bridges over Intersections in Thailand

This paper overviews the recent project launched by the Bangkok Metropolitan Administration (BMA) as a part of the maintenance program to investigate the safety, remaining fatigue life, and serviceability of steel bridges over many intersections in Bangkok. A total of eleven steel bridges, which belong to the slab-on-girder type, were inspected and a full-scale nondestructive load test was conducted to investigate the bridge actual behaviors and validate the three dimensional finite element modeling. The remaining service life is based on the fatigue life assessment which consists of continuous measurement of traffic and strain data for about one week.