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23 damage at the dowel-concrete interface that occurred during The repeated shear load testing also revealed that the shear the pullout test. capacity of a dowel subjected to repeated loading was sig- Figure 3.10 shows the relative dowel displacement versus nificantly lower than that for a dowel subjected to a single shear force for dowels with various embedment lengths. This displacement-controlled loading. A comparison of shear force figure shows that reducing the embedment length from 9 in. versus displacement for a 2 in. [51 mm] vertically translated [229 mm] to 6 in. [152 mm] had little effect on dowel shear dowel (i.e., with concrete cover of 1.25 in. [32 mm]) to that of behavior, reducing the embedment length further to 4 in. an aligned dowel (i.e., with concrete cover of 3.25 in. [83 mm]) [102 mm] had little effect on shear stiffness but resulted in a shows that (1) the shear stiffness of both dowels was reduced large reduction (26%) in shear capacity. Further reducing the after 14,000 load cycles and (2) the stiffness of the 2 in. [51 mm] embedment to 3 in. [76 mm] produced an additional 12% vertically translated dowel exhibited a secondary decrease as reduction in shear capacity (38% total reduction with respect the load approached 3 kips [13 kN] (as shown by the rapid to the 9-in. [229 mm] embedment condition) and a 63% decrease in slope of shear load versus displacement curve above reduction in shear stiffness. The reduction in embedment to 2.5 kips [11 kN]). This observation suggests that failure of the 2 in. [51 mm] resulted in shear capacity and shear stiffness of dowel with reduced concrete cover and subjected to repeated 56% and 30%, respectively, of the values for 9 in. [229 mm] loading started at loads approaching 3 kips [13 kN], which is embedment. significantly lower than the failure due to single load applica- The average shear capacity values for aligned dowels and tion of 4.7 kips [21 kN]. dowels with concrete cover reduced from 3.25 to 1.25 in. Single load tests showed that reduced dowel diameter causes [83 to 32 mm] due to vertical translation of 2 in. [51 mm] lower shear stiffness. Similar shear performance trends were were 9.3 and 4.3 kips (42.2 and 19.1 kN, respectively). Thus, noted for aligned dowels and dowels with reduced concrete the ultimate shear capacity was reduced by more than 50% covers. As expected, lower shear capacity and shear stiffness due to this reduction in concrete cover. were measured for the 1.25-in. [32-mm] diameter dowels than those for 1.5-in. [38-mm] diameter dowels with the same When comparing the shear force versus relative dowel alignment. displacements for an aligned dowel to that for a dowel with The effects of dowel misalignment on performance observed reduced embedment length, a dowel with reduced concrete in the laboratory study can be summarized as follows: cover, and a dowel with both reduced embedment length and reduced concrete cover, a compounding effect of misalign- Presence of greasing significantly affects pullout force. ments is observed. The decrease in concrete cover results in a Dowel rotation as extreme as 2 in. per 18 in. [51 mm per large decrease in ultimate shear capacity with little loss of 457 mm] does not affect dowel shear capacity. shear stiffness while the reduction in embedment results in Reduction of dowel embedment length to 3 in. [76 mm] or modest losses of both shear capacity and stiffness. However, the less significantly affects shear capacity. combination of both misalignments results in large reductions Reduction in concrete cover from 3.25 to 1.25 in. [83 to in both ultimate shear capacity and shear stiffness. 32 mm] causes large reduction in ultimate shear force. The combined effect of low concrete cover and low embed- ment length is greater than the effect of either one of the 12000 two misalignments. 9 in. embedment 10000 6 in. embedment 3.3 Analytical Modeling 4 in. embedment 8000 The ABAQUS beam-dowel model presented in Chapter 2 Shear Force, lbs. 3 in. embedment was used to perform computer simulations to augment the 2 in. embedment 6000 results of the laboratory study and to further investigate the effects of dowel misalignment on joint behavior. 4000 3.3.1 Finite Element Beam Model 2000 A validated beam model will allow consideration of dowel 0 misalignment cases other than those tested in the laboratory. 0 0.02 0.04 0.06 0.08 0.1 0.12 The shear force required to cause 0.05 in. [1.3 mm] of relative Relative Displacement, in. displacement was defined as the dowel shear capacity because Figure 3.10. Effect of embedment length on shear the shear force required to cause this displacement according force versus displacement. to the analytical model was similar to the shear capacity level