Beenay Shahi

how to model brick masonry walls in etabs? how to model reinforced concrete frame with brick masonry infill in etabs? I want to design a soft story building of four story with reinforced concrete frame with brick masonry infills. If I can model brick masonry wall, I might be able to design soft story building by dynamic analysis, by modelling the walls in first, second and third story and no walls in ground story. This is the first method suggested by the IS code. ie: "7 .10. l In case buildings with a flexible storey, such as the ground storey consisting of open spaces for parking that is Stilt buildings, special arrangement needs to be made to increase the lateral strength and stiffness of the soft/open storey. 7.10.2 Dynamic analysis of building is carried out including the strength and stiffness effects of infills and inelastic deformations in the members, particularly, those in the soft storey. and the members designed accordingly." I tried to use the second method ie: "7.10.3 Alternatively, the following design criteria are to be adopted after carrying out the earthquake analysis. neglecting the effect of infill walls in other storeys: a) the columns and beams of the soft storey are to be designed for 2.5 times the storey shears and moments calculated under seismic loads specified in the other relevant clauses: or, besides the columns designed and detailed for the calculated storey shears and moments, shear walls placed symmetrically in both directions of the building as far away from the centre of the building as feasible; to be designed exclusively for 1.5 times the lateral storey shear force calculated as before." to increase the base shear by 2.5 times, I had to set mass source factor as 6.5 ie: 6.5(DL), 6.5 (wall load), 6.5(floor finish) and 6.5x0.25(liveload) .multiplying the mass source by 2.5 didn't increased the base shear much. hence i was able to achieve 2.5 base shear by increasing the seismic weight by 6.5 times. by doing so I got reinforcement for a column to be 6200 sq. mm. which was 1200 sq mm in normal analysis. are my results plausible? And code aslo suggests that the columns and beams of the soft storey are to be designed for 2.5 times moments calculated under seismic loads specified in the other relevant clauses besides the storey shears. by multiplying the normal mass source by 6.5 times, base shear has increased by 2.5 times but I don't know if the moments are also increased by 2.5 times or 6.5 times of by any other factor . Actually on checking that column I found that in the normal case Mu2 for that was 72 KNm. While for the mass source increased by 6.5 times, it was 211 KNm. So, moment in the column has increased by 211/72=2.93 times. Can somebody tell me how to design soft story building?

According to IS code soft story should be design with 2.5 times the base shear. So, I multiplied the mass source factor by 2.5 in etabs. but base shear didn't even increased to twice. Maybe I should increase the mass source factor until the base shear of soft story building is 2.5 times that of normal building. I have many questions? Am I doing it right? Is my understanding correct. Is there more appropriate method to do it? Are columns only structural elements I should separately design for for soft story? or I should design beams and slabs too for soft story. Please somebody clarify my questions and suggest best way to design building with soft story. and also common errors and misunderstanding regarding such design?

If i analyze my model with default mass source I.e. element mass and additional mass it will be incorrect? Because it won't include the live load and other loads like floor finish and wall load in the calculation of earthquake load. So I must define the mass source as specified load pattern and define load patters as 1 DL+1 floor finish+1 wall load+0.25 live load. And I must select the options: include lateral mass and lump lateral mass at story level Please tell me whether I am right or wrong? But I have some doubts and questions too. what does etabs consider as "additional mass"? does additional mass include the loads we define as live load, wall load, and floor finish? I know that etabs refer to "element mass" as the mass of the structural elements we used to model the structure like beam, column, slab for which we define the material and section properties. What does the option include lateral mass do" what is lateral mass? Is lateral mass something we define of is it something etabs calculate from our model?

Thank you for the suggestion but I have only assigned supports for base and I have rechecked it.

Thanks a lot engruzair!

one of my friends told me that the width of strap beam should be greater than the column width. I don't know on what basis he said that. I don't think its true. I have designed a strap footing of width 9 inches and depth 22 inches. Do dimensions of my strap beam goes against any code? Or I can design the strap beam just as other beams in superstructure such that B/D is not less than 0.3.

using staad foundation advanced, I designed a strap footing for two eccentrically loaded columns(offset of left column=-600mm and offset of right column=600mm) of one bay, 3 storey building with grid spacing of about 14 ft in x direction and 12 ft in y direction. The dead load was about 300kN and live load was about 60 KN and earthquake load was about 40 KN in -y direction with moment about z axis 25 KNm. soil bearing capacity was 150 KN/m^3. I used the load combination 1DL+1LL and 1DL+0.8LL+0.8EL. strap beam was in x direction. I got footing size 1.75mx1.75m. footigg thickness 200mm. no of 12mm bars in x direction=6 and no. of 12mm bars in z direction=23. I got doubly reinforced strap beam with 0.53m depth and 9 inch width. bottom reinforcement=3 no. of 12mm bars top reinforcement=6 no. of 16mm bars. And for shear reinforcement it says:"Since nominal shear strength of concrete is greater than maximum shear force, shear reinforcement is not required". I just want to know are the results I got practical or is it likely that I had made some mistakes. I have doubt whether the following result in right or wrong: the vast difference of reinforcement in x and z direction which are 6 and 23 no. of 12mm bars respectively for 1.75mx1.75m footings. and another doubt is requirement of no shear reinforcement in strap beam. and my another question is the load combination I am using is sufficient for footing design or not? Please help me!

using staad foundation advanced, I designed a strap footing for two eccentrically loaded columns(offset of left column=-600mm and offset of right column=600mm) of one bay, 3 storey building with grid spacing of about 14 ft in x direction and 12 ft in y direction. The dead load was about 300kN and live load was about 60 KN and earthquake load was about 40 KN in -y direction with moment about z axis 25 KNm. soil bearing capacity was 150 KN/m^3. I used the load combination 1DL+1LL and 1DL+0.8LL+0.8EL. strap beam was in x direction. I got footing size 1.75mx1.75m. footigg thickness 200mm. no of 12mm bars in x direction=6 and no. of 12mm bars in z direction=23. I got doubly reinforced strap beam with 0.53m depth and 9 inch width. bottom reinforcement=3 no. of 12mm bars top reinforcement=6 no. of 16mm bars. And for shear reinforcement it says:"Since nominal shear strength of concrete is greater than maximum shear force, shear reinforcement is not required". I just want to know are the results I got practical or is it likely that I had made some mistakes. I have doubt whether the following result in right or wrong: the vast difference of reinforcement in x and z direction which are 6 and 23 no. of 12mm bars respectively for 1.75mx1.75m footings. and another doubt is requirement of no shear reinforcement in strap beam. Please help me!

the link you provided won't open.

isn't length of stirrup required to calculate the spacing of shear reinforcement?

the problem is that no column has failed and etabs gives so little reinforcemenr of about 743mm for all columns which are 12"x12" in size and concrete grade is M20.

Thank you very much for the clarification!

should strap beam merge with the isolated footing to be the strap footing together? Or, can I cast the strap beam above the isolated footing so that there is a gap between isolated footing and the strap beam?

well i designed a residential building in etabs which is two bay in both x and y direction. actuall 4 bay in y direction including two bays of very small span of about 5 ft. the bays in both direction is of about 12ft. its two and a half storey. Its pretty much a average normal residential rcc building. all columns are 12"x12" m20 concrete. beams are 9"x14" m20 concrete. slab is m20 5inch thick. reinforcement is hysd grade 500. live load in all rooms 2 kN except in the staircase slab and balcony slab which is 3kn and floor finish for all floors 1kn. wall loads in exterrior walls without opening is 9.09km/m. wall loads in exterior walls with openings is 6.36kn/m. interior walls 3.51km/m. paraphet walls 2.18 kn/m. eq load according to indian code zone v seismic area. but etabs gives very little reinforcement for my columns. and reinforcement on all columns are same. its 743mm^2. I have remodelled it and redesigned it in etabs for at least 10 times but same result. Its a recent problem in etabs 2015. sometimes back it used to give the practical reinforcement in columns. I don't know whats the reason for the wrong result in etabs. for such a residential building the reinforcement area for middle column should have been 1600mm^2 and for the edge column 1200mm^2 and for corner columns 900 mm^2. Please somebody check my etabs model and help me find whats the matter. is it something wrong with my model or its software? bouse for Mr. Rupendra Bista.EDB bouse for Mr. Rupendra Bista.bmp

My Etabs 2015 Gives Very Little Reinforcement For The Columns Of My Rcc Building. What Might Be The Reason. My Etabs File Is Attached Herewith. https://www.dropbox.com/s/gy1ndwqau32dq64/house%20for%20rupendra%20bista%208.EDB?dl=0 house for rupendra bista 8.EDB

bouse for Mr. Rupendra Bista.EDBin etabs reducing the property modifier 'moment of inertia in 1 and 2 direction' to 0.35 for concrete beam drops reinforcement required in beam to minium. And when increasing the moment of inertia of concrete beam section in 1 and 2 direction, reinforcement required in beam increases while that for column drops to minimum required. why? please somebody explain it to me. Thanks in advance? here is a residential building attached here with. why is the reinforcement in beam so low? is it a practical result?

Please help me in understanding what is load size in csi safe footing design. What data should i input in load size?

I am also having problem in understanding the results. I have attached here a picture of an elevation of a building with the shear reinforcement result generated by etabs. There are three values of shear reinforcement for each beam and 2 values(which are duplicates) for column. What do those values mean. For example one of the value is 594.34. So, how do i calculate what diameter stirrup to use use at what spacing. Similarly, shear reinforcement values are higher for the cantilever beams of balcony which i projected 4ft outwards. Are those normal values for 14ft by 10ft rooms. All beams are 9"x14" and all columns are the etabs model and bmp image of shear reinforcement results are attached herewith. chundevi madhyamik etabs.rar