Research On The Evaluation Of Strength For Fired Brick In Existing Masonry Structures By Rebound Method

With its nondestructive, simple, faset attributes, as well as its wide range of application, avaluation the compressive strength of brick in a masonry structure by using Rebound Method, is an ideal in-situ methonds. With the wide application of Rebound Method, the relevant national standard and industry standards , as well as the local strength calculation curves are established. The application of strength calculation formula provided in the national stand"Technical standard for inspection of building structure"(GB/T50344-2004)is limited, due to its inaccuracy and the necessity of sampling; The inaccuracy of the Rebound Test can also be causede by the misapplication of the industry standard"The method of evaluation the fired common brick strength grading by rebound method"(JC/T796-1999)in the calculation of the rebound value in the in-situ Rebound Test; In addition, there is no corresponding standard for the Rebound Test of the fired perforated birck being increasingly widely usded. For these reasons, it is necessary to establish the nationwide unified strength calculation formula for the calculation of rebound value of fired common brick and fired perforated brick. Based on the comparison of the existing relevant standards ,the experimental results, and on the mathematical statistics method , a general formula of strength calculation for fired common brick and fired perforated brick in existing masonry is established . The main works are summarized as follows:(1)The basic principles and influencing factors of the Rebound Method for brick inbuilt in the existing masonry are introduced; Based on the comparative test of 6 standard masonry specimens and 12 specimens for compressive strength test of fired perforated brick , the influence of vertical load and constraints on the rebound value is analyzed.(2)According to the strength calculation formulas provided in the current 3 local standards, 37 rebound values (range from 30 to 48) are converted respectively to the corresponding compressive strength, then 111 data of rebound value(R)–compressive strength (f ) can be obtained. The data of R-f is fitted with the Least Square Method in the style of parabolic function , the strength calculation formula for the fired common brick in the existing masonry can be obtained .(3)According to 2 different test method , the rebound test and compressive strength test for 3 standard masonry specimens and 141 specimens of fired perforated brick are carried out.The 209 data of R-f obtained from the Rebound Test and the compressive test are divided into 23 groups by group interval of 0.5 , the average value of rebound value and compressive strength in each group are calculated. The 23 average value of rebound value and compressive strength, and 10 data of R-f obtained from the test of Henan Institute of Building Research totally come to 33 data , which is fitted with the Least Squred Method in the style of power function .Then the strength calculation formula for the fired perforated brick in the existing masonry can be obtained.The experimental results shows that the accuracy of the general formula of strength calculation for the fired common brick and fired perforated brick in existing masonry is high, which can provide the basis for the for the revision of relevant standard.