دانلود رایگان مقاله ارزیابی قوانین EC2 برای طراحی اتصالات فشرده سازی اتصال لبه روی لبه

ABSTRACT

This paper presents an evaluation of EC2 rules for design of compression lapped joints based around a database of approximately 150 individual test results reported in the literature. A comparison is provided between tension and compression laps, and a review of semi-empirical and empirical expressions reported in the literature is presented. Compared to laps of bars in tension, the influence of minimum concrete cover on compression lap strength is low or negligible, but the influence of transverse reinforcement is stronger. The performance criteria for lapped joints are discussed, and a difference noted between compression and tension laps. The evaluation has been carried out by first determining the lap length required by EC2 to develop the design strength of a bar, and the strength of that lap then estimated using three different semi-empirical expressions each derived from part of the database. The outcome shows that EC2 procedures provide a greater margin of safety for compression laps than for tension laps. The margin of safety against failure of compression laps designed in accordance with EC2 is found to be broadly consistent with expectations for a concrete cover equal to one bar diameter, but reduces at larger cover/bar diameter ratios. Consequently it is recommended that for compression laps coefficient α2 be independent of cover ratio and set to 1.0.

6. Conclusions and recommendations

1. End bearing makes an appreciable contribution to strength of lapped bars in compression. 2. The influence of minimum concrete cover or clear spacing on strength of compression laps is much reduced in comparison with tension laps, consequently coefficient α2 in Table 8.2 of EC2 should be taken as 1.0 for compression laps. 3. The influence of transverse reinforcement is greater for compression laps than for tension laps, hence there is no valid reason for setting coefficient α3 in Table 8.2 of EC2 at a more conservative value than for tension laps. 4. The margin of safety against failure of compression laps designed to EC2 is around 8% less than might be expected, but in the absence of reported failures may be considered adequate. 5. Due to the contribution of end bearing, the strength of compression laps is not proportional to lap length. Consideration should be given to reformatting rules for assessment of existing structures with lap strength calculated as the summation of contributions from bond and end bearing. 6. Design rules should identify situations in which end bearing may be reduced by minimum cover to the end of a bar. 7. It is recommended that a more detailed statistical analysis be conducted taking account of the variability in both bond resistance as estimated by Eqs. (2), (3) and (5) and in parameters relevant to the failure criterion for compression laps proposed here. 8. It is noted that Table 8.2 and Eq. 8.10 of EC2 appear inconsistent, and it is recommended that a correction be introduced.