ANALYSIS OF MOMENT RESISTING FRAME & LATERAL LOAD DISTRIBUTION LATERAL LOAD DISTRIBUTION OF FRAME BUILDING: • In a two dimensional moment resisting frame each joint can have at the most three degrees of freedom (displacement in horizontal and vertical directions and rotation). • To tal number of degree of freedom is 3Nj where Nj is the number of joints in the frame. • In practice, beams carrversmall a!ial force and undergo negligible a!ial deformation. This means horizontal displacement at all joints located at the beam level s same. • In most buildings uptown moderate height, the a!ial deformation of columns is negligible. • Numbers of degrees of freedom are reduced to one rotation and one horizontal displacement. • "s the rotati onal inertia associ ated with the r otational degree of freedom is insigni ficant, it is further possible to reduce, through static condensation, the number of degrees to one per storeforcarring out dnamic analsis.• In similar wa, each joint of three dimensional frames can have at most si! degrees of freedom. • #inall, there are three degrees of freedom per floor. • #ree vibration analsis of the building can thus be carried out bsolving (3N$3N) %igen value problem, where N is the number of stores in the building. • &nce natural fre'uencand more shape is nown it is possible to obtain the ma!imum seismic force to be applied at each storelevel due to given earth'uae ground motion. LAT ERAL LOAD ANALYSIS OF MOMENT RESISTING FRAME: • &nce the design lateral loads are nown on the twodimensional frames, one could analze the frame for the member forces. • &ne could carrout an accurate computer analsis or an appro!imate analsis as per re'uirement. • "ppro!imate anals is is usuallper formed at preli minardesign stage and to assess the computer analsis. • Tw o commonlused methods*A. Portal frame method: Frame* +ortal framesare fre'uentlused over the entrance of a bridge and as a main stiffness element in building design in order to transfer horizontal forces applied at the top of the frame to the
8
Embed
30 - Analysis of Moment Resisting Frame and Lateral Load
Design Basis for Analysis of Moment resistant frame
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
7/21/2019 30 - Analysis of Moment Resisting Frame and Lateral Load
columns. 4an engineers arbitraril define the location at h53 (#ig. 3(b)), and therefore place hinges
at these points, and also at the center of the girder.
#ig. 3 +ortal frame partiall fi!ed at base
Tr$ed Frame* 6hen a portal is used to span large distances, a truss ma be used in place of
the horizontal girder. -uch a structure is used on large bridges and as transverse bents for large
auditoriums and mill buildings. " tpical e!ample is shown in #ig. 7(a). In all cases, the suspended
truss is assumed to be pin connected at its points of attachment to the columns. #urthermore, the
truss eeps the columns straight within the region of attachment when the portals are subjected tothe sideswa 8, #ig. 7(b). onse'uentl, we can analze trussed portals using the same
assumptions as those used for simple portal frames. #or pinsupported columns, assume the
horizontal reactions (shear) are e'ual, as in #ig. (c). #or fi!edsupported columns, assume the
horizontal reactions are e'ual and an inflection point (or hinge) occurs on each column, measured
midwa between the base of the column and the lowest point of truss member connection to the