Distribution of Forces in Tension Bolt

Figure 8(a) shows the distribution of internal forces in tension bolt for the case of model FE12np, in which initial pretension force introduced in bolts is ignored. The total tensile force surcharged to the

Fig. 8. Distribution of forces in tension bolt.

bolt for this case is evaluated as the summation of shear force applied to the top angle (hereinafter, shear force) which is equivalent to the tensile force applied to the upper flange of beam, and prying force because no pretension is applied to the bolts. From this figure, it can be observed that tensile force applied to the bolt is almost one and half time as much as shear force up to near the ultimate state. If the bending stiffness of top angle were infinite, tensile force applied to bolt would be equal to shear force applied to the angle.

It is apparent that prying force is also subjected to the tension bolts in case introducing pretension of model FE12 (Figure 8b). However, it is difficult to estimate the prying force subjected to tension bolts because bolt force consists of three components: shear force applying to top angle, contact force due to bolt pretension, and prying force. The shear force is determined as the transferred force from beam flange, whereas the other two forces can be determined as contact force that is the summation of contact force due to bolt pretension and prying force. In this study, to classify the contact force into the two forces, it is assumed that the distribution of prying force corresponding to shear force in case considering bolt pretension is similar to that for case ignoring pretension forces in bolts because it is confirmed that distribution of prying force in both cases considering with/without pretension forces in bolts is almost the same according to the results obtained from pre-analysis for investigating the influence of bolt pretension on prying action. Figure 8(b) shows the distribution of forces subjected in tension bolt of model FE12, which is the case by considering pretension forces in bolts. It is seen that three components of bolt force can be properly estimated. From this figure, it is observed that the contact force component caused by pre-tensioning of bolts is decreased nonlinearly with increasing of the shear force applied to the top angle’s vertical leg.