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  1. Blackstar123

    Sustained part of the governing load combination in ßdns

    Governing Seismic combination for column design is this: Pu = (1.2 + 0.2Sds)D + 0.5L + Eh As per ACI 318 Section 6.6.4.4.4. My question is what we should take as sustained part of the load combination for calculating βdns, 1.2D or (1.2 + 0.2Sds)D. I usually take it as 1.2D, because as I...
  2. Blackstar123

    Use steel on compression face to Increase phi Mn?

    I have a two story RCC structure with multi bays in X direction and single bay in Y direction. The building LRFS is IMRF. Flexure demand on the beams in Y direction due to seismic loads is coming out to be very high such that some compression reinforcement will be required for -Mu. The span of...
  3. Blackstar123

    Looking for ACI reference of the attached formula

    I'm reviewing the design calculation of anchoring to concrete checks, submitted by another design firm. The designer has calculated the pull out capacity of L bolts using the following formula, which is contrary to the one given in Chapter 17. I am having difficulty finding out the reference...
  4. Blackstar123

    This is unreal..

    Is This real? Am I the only one who is having a hard time believing my eyes. There seem to be at least a total of 5 cantilever floors for office use may be? I can't seem to find the name of this building or any other relevant information. It showed up in google search while I was searching...
  5. Blackstar123

    Maximum Force a Compression Brace can carry just before it "Buckles"

    A steel braced frame for seismic loads is designed such that any inelastic response occurs in the “braces”. These braces are usually arrange in opposing pairs so that when a brace has buckled in compression, the tensile strength of the other brace is enough to support the earthquake loads. If...
  6. Blackstar123

    How to reduce torsion on the beam?

    I've a structure supporting a steel silo. I've calculated forces on the supporting beam assuming the load path as shown in attached Figures. I'm trying to pass the supporting beams in torsion, which is coming out to be quite large due to heavy load (Tu = 130 KN-m = 1145 kip-in). There's a...
  7. Blackstar123

    Lever Arm for Stiffened End Plate Moment Connection

    Follow up question from thread507-220851 Situation describe in referenced thread is somewhat similar to at AISC design example 8ES. Contrary to believed opinion of most contributors, lever arm consider in this example to determine the couple force is d-tf, even though the end plate stiffener is...
  8. Blackstar123

    Design load for column/joint retrofitting in case of Strong Beam-Weak Column behavior

    BACKGROUND INFO I am checking the design of an existing G+1 building with a total plan dimension of 25m (L), 9m (W) and a height of 14.8m, as shown in following fig. There is a standard live load of 100 psf on first floor and, equipment loads (provided by supplier) at roof level. The height...
  9. Blackstar123

    To retrofit, or not to retrofit?

    I am checking the design of some RCC beams. The required bottom reinforcement at supports due to seismic load combination is coming out to be less than the minimum reinforcement. Code specifies that in such a case, beam should at least have As = 1.33 times the required reinforcement. However...
  10. Blackstar123

    Plastic section modulus of a composite section

    I am trying to verify cross-sectional properties calculated by Section designer in sap2000 with different base material and material of shape. For this exercise I've defined A36 as base material and C30 as material of the shape inside the section designer. I've verified cross-sectional...
  11. Blackstar123

    Identify the lateral load resisting system

    I'm having difficulty in identifying the type of lateral resisting system for the following frame. Should I called this a moment frame or a Cantilever Column? If I look at the moment diagram for combine load cases, I'll identify the following first two cases as moment frame. But again for the...
  12. Blackstar123

    Concrete Jacketing

    Due to increase in load on existing structure, I need to increase the size of the foundation (combined footing) and the concrete pedestal through concrete jacketing. I am looking for ACI code provisions for design of shear keys such as diameter of holes, depth, spacing, shape of bar etc. Any...
  13. Blackstar123

    Seismic performance of infill frames

    This is a question that always pop into my mind when I see a 10+ story RCC building, with all stories filled with masonry infill walls except those floors which are reserved for parking. How do they take into account the effect of masonry infill in the seismic analysis of the frames? My major...
  14. Blackstar123

    Steel Connections weaker than Members in Seismic Analysis

    I am checking the design of an existing steel structure. This is an industrial building which was originally designed for UBC seismic zone-2A. But now clients want to check if the same design will be able to resist the UBC seismic zone-2B earthquake forces. A number of steel members have design...
  15. Blackstar123

    Secondary beams in ETABS

    Hi all I am confused about secondary beams option in ETABS. As to my knowledge, secondary beams are those which rest on another beam (called primary beam). These beams have pinned supports unlike other beams which have continuous moment release. My 1st question is what if i draw a "secondary...

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