**5. Discussion of the single-bay, single-story model analysis results**

Pushover analysis of single-bay, single-story infilled frame with fuse element model was carried out to compare the response with infilled frame without fuse element. The results of this analysis are shown in **Figure 9** along with the results from the experimental study of the bare frame and infilled frame. For better clarity, **Figure 14** shows the plot of the initial deflection portions with larger scale. The effect of varying the fuse capacity on the system response is illustrated in **Figure 9** with three different values for the fuse capacity (i.e., 89 kN, 178 kN,

**Figure 14.** Load-deflection relation for single-bay, single-story model with "brittle-failure" fuse element [53].

and 267 kN). The figure shows two stages of response consisting of (a) prior to breakage of the fuse and (b) after breakage. During the first stage shown by line OA in **Figure 14**, the fuse transfers lateral loads from the frame to the infill wall and as such, the slope of the line OA represents the combined larger stiffness of the steel frame and the masonry infill wall. Upon breakage of the fuse at point A (capacity of fuse), there is sudden drop in the force level, line AB, followed by load-deflection relation along BC, which represents the response of the bare frame. This means that the infill wall is disengaged from the steel frame and only the bare frame is resisting the total load.

Comparison of the response of the model having fuse element with those of the bare frame and infilled frame in **Figure 9** shows that the stiffness of the system with fuse element is slightly smaller than that resulting from tested infilled frame (about 75% of the infilled frame). This, however, is about ten times the stiffness of the bare frame. Although as shown in **Figure 9**, higher strength fuse elements increase the strength capacity of the system, but it should be noted that the objective is to prevent failure of the wall. For example, based on the test results (shown on the figure), the tightly fitted masonry infill wall cracks around a lateral load of 378 kN. The smaller the fuse capacity, the larger will be the margin of safety against cracking.

The fuse element model shown in **Figure 13** describes a condition where upon breakage of the fuse, the force transfer across the fuse becomes zero. Since this could imply a shock-type response, but which is more like cracking of reinforced concrete or masonry system, it is possible to develop fuse elements that show more ductile response. For example, if the fuse element can be described by the trilinear or multilinear models shown in **Figure 15**, the corresponding load deflection plots for the infilled frame will be those shown in **Figures 16** and **17**, which show a more gradual drop of the force across the fuse and a smoother transition to the bare frame condition. It should be noted that depending on the mechanism of failure or design function of the fuse, different types of infilled frame response can be obtained. Examples of such mechanisms could include friction damper mechanism for energy dissipation and enhanced seismic response of the structure.

**Figure 15.** Assumed force-deformation responses for fuse element (a) "trilinear" and (b) "multilinear" [53].

**Figure 14.** Load-deflection relation for single-bay, single-story model with "brittle-failure" fuse element [53].

to simulate the condition of fuse breakage with subsequent zero force in the element, once the fuse capacity is reached. The fuse capacity is a function of the masonry infill wall shear strength. According to test results in Ref. [56], the infill wall had a capacity of 383 kN, which with a factor of safety of 4.0, yields a fuse capacity of 89 kN for the model. This value was used to specify FSLIDE, for which a negative value results in a drop to zero when the force in the element reaches the specified capacity (89 kN), while a positive value represents yielding or constant

force equal to the capacity. In this case, only negative value was assigned.

40 New Trends in Structural Engineering

**5. Discussion of the single-bay, single-story model analysis results**

Pushover analysis of single-bay, single-story infilled frame with fuse element model was carried out to compare the response with infilled frame without fuse element. The results of this analysis are shown in **Figure 9** along with the results from the experimental study of the bare frame and infilled frame. For better clarity, **Figure 14** shows the plot of the initial deflection portions with larger scale. The effect of varying the fuse capacity on the system response is illustrated in **Figure 9** with three different values for the fuse capacity (i.e., 89 kN, 178 kN,

**6. Discussion of the two-bay, three-story model analysis results**

**Figure 18.** Two-bay, three-story model description [53].

(c) three-diagonal strut method [53].

With the finite element model validated based on the performance of a single-bay, singlestory infilled frame, the modeling approach can next be applied to a multi-bay, multistory system. The same modeling features presented in previous sections were used to model the two-bay, three-story frame shown in **Figure 18**. The panel dimensions and material properties were the same as those for the single-bay, single-story case. The steel frame members,

Finite Element Modeling of Masonry Infill Walls Equipped with Structural Fuse

http://dx.doi.org/10.5772/intechopen.77307

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**Figure 19.** ANSYS models for two-bay, three-story case study: (a) bare steel frame; (b) single-diagonal strut method; and

**Figure 16.** Load-deflection relation for single-bay, single-story case study with "trilinear" response for fuse element [53].

**Figure 17.** Load-deflection relation for single-bay, single-story case study with "multilinear" response for fuse element [53].
