For all types of studied pipes, it was observed that the variability of the cracking load
([F.sub.cracking]) was greater than the rupture load ([F.sub.maximum]).
The ultimate load ([F.sub.u]), the yielding load ([F.sub.y]), and corresponding deflections ([d.sub.u], [d.sub.y]), as well as the cracking load
([F.sub.cr]) and the displacement ductility ratio (D), defined as the ratio of midspan displacement at the ultimate load ([d.sub.u]) to the midspan displacement at the yield of reinforcement ([d.sub.y]), are given.
In the pictures, burst-mode cut-through failure instead of obvious progressive crack growth was observed, for the briquette coal samples, cracks generated were not obvious at the early stage, but suddenly increased when the load imposed was near the cracking load
. In this case, when the two types of samples were close to failure, the number and width of the newly generated cracks, bending complexity of the cracks, and roughness of the cracks' interior in the raw coal samples were obviously greater than those in the briquette coal samples.
The cracking load
, yielding load, and ultimate load of the Beam B-CR and B-MS were less than that of B0 due to initial damage.
So in author's opinion it is better to accomplish prestressing when the external load is near the cracking load
value, with the condition that the tensioned part of the section is cracked.
Compared with SRC beam, there is inverted-arch deflection before loading in PSRC beam, and the cracking load
is improved, so the cracking load
of PSRC beam is 68 kN; the cracking load
of SRC is only 26 kN; it can be confirmed that the prestressed force can improve load carrying capacity of the beam under service load conditions.
When the cracking load
is reached, the vertical bending cracks appear in the beam region close to the core area, the crack width is about 0.05 mm, and it is completely closed after unloading.
The initial cracking load
for both FE beam and experimental beam was 18.75 KN and the final cracking load
was 86.8KN and 86KN respectively which was in harmony.
If the fiber volume fraction is higher than the critical fiber volume fraction, the fibers will be able to sustain the cracking load
, and multiple cracking will occur.
With the measured initial cracking load
and the depth of the precutting crack of the three-point bending beam specimen, the initial fracture toughness of the concrete containing nano-Si[O.sub.2] and flyash can be calculated as follows :
Table 3 shows the variation of diagonal cracking load
([P.sub.cr]), flexural crack load ([P.sub.fl]) and ultimate load ([P.sub.u]) of beams having varying tensile/compression reinforcement ratios and transverse reinforcement spaces.
According to the test results and the finite element analysis results, 1:3 model joint cracking load
is 2000 kN, which is twice the design load.