Assignment #6 - Miranda PDF

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Miranda...

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Prof. Eduardo Miranda

CE285B Advanced Structural Steel Behavior and Design

! ASSIGNMENT 6 Due Monday Mar 5th, 2018 You are asked to design one of the moment resisting frames located on the transverse direction of a 10story building shown in the figure. A table of equivalent static forces to be applied on each frame is given below. These forces are already reduced using a reduction factor R=8.0. For the analysis you may use ETABS. Using AISC LRFD you are required to design beams and columns using A992 steel and W14 sections for the columns. For the beams you may consider decreasing depths along the height of the building. The story height in the first story (ground story) is 17 ft and 15 ft for the rest of the stories. Location for the column splices is shown in the figure and at 6ft from the intersection of the beam-column joint of the level below. For the design of beams and columns consider the following combinations: (a) 1.2D+1.6L; (b) 1.2D+0.5L+E. In second load combination L is the unreduced live load. For the gravity loads assume the following loads: slab (deck and concrete) 60 psf, ceiling and MEP 10 psf, self weight of the structural system (beams, girders and columns) 10 psf. Live load 60 psf. Make sure that beams and columns are able to carry the worse of the two load combinations previously mentioned, that satisfy the strong column weak girder equation explained in class and that you do not exceed a maximum interstory drift ratio of 0.02 in any story. To compute the maximum interstory drift ratio you need to multiply the interstory drift ratio computed with the reduced forces times a factor Cd=5.5 before you check against the 0.02 limit. In your analysis you may consider the beam column joints as rigid and consider P-delta effects. Watch this video if you want to learn about how you may want to consider P-delta effects in your preliminary design: https://www.youtube.com/edit?o=U&video_id=rxBfC4MdWu0 You are asked to: (a) Provide an elevation of the frame indicating very clearly the sections you have chosen; (b) Plot the lateral displacement (multiplied by Cd) along the height of the building (deflected shape); (c) Plot the interstory drift ratios (multiplied by Cd) along the height of the building; (d) Design the RBS interior connection (with two moment connections at each side of the column) at the second floor. Use the 2010 ASIC seismic specifications and the 2010 AISC/ANSI 358 standard. Provide all calculations.

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PLAN

ELEVATION

FLOOR ROOF 10 9 8 7 6 5 4 3 2 1

For the 1. 2. 3.

HEIGHT [ft] 152.0 137.0 122.0 107.0 92.0 77.0 62.0 47.0 32.0 17.0 0.0

Force [kips] 62.69 53.48 44.79 36.65 29.09 22.16 15.91 10.42 5.79 2.20 0.00

Shear [kips] 62.69 116.17 160.96 197.61 226.70 248.86 264.77 275.19 280.98 283.18 283.18

analysis you are asked to consider the following modeling assumptions: Consider the columns fixed at the base of the frame. Model the splices as located six feet above the intersection of beam and columns. Consider the panel zones as rigid. As discussed in class in reality there is additional flexibility due to the actual stiffness of beam column joints. This overestimates the stiffness of the lateral resisting frame, but on the other hand we are not considering the lateral stiffness from the rotational stiffness of shear connections in the gravity system. (In an actual design I recommend that you account for the flexibility of the connections and of the rotational stiffness of the gravity system, you can read more about this in the optional reading by Charney and Downs for beamcolumn modeling and Liu and Astaneh for shear connection modeling). 4. Do not reduce the beam stiffness due to the presence of the reduce beam section. In reality, once you reduce the flange width in a portion of the beams, they will no longer be prismatic (constant properties along the length) and the flexural stiffness will be reduced (roughly by 10%). However, composite action will increase the stiffness of the beams by a small amount when the slab is in tension and by a greater amount when the slab is in compression. The net result will be roughly the average increment in stiffness from positive and negative bending stiffnesses. This means that the reduction in stiffness due to the reduced beam section is at least partially compensated by the increase in flexural stiffness from composite action. For the homework we are simplifying the modeling by using a prismatic element with stiffness equal to the steel shape with no composite action. 5. Only model the lateral resisting frame (do not model the gravity columns)....