Waqar Saleem

apply same modifiers in safe as in etabs then check

Thought provoking article, however there are a few queries which need further consideration: (1) The reinforcement is always being provided in slabs for negative moment both along the beam and perpendicular to beam. Due to availability of sophisticated software’s such as ETABs and SAFE, this reinforcement is provided based on compatible behavior of slab and beams. Moreover, concrete shall crack in tension (may be at service level gravity loads) and reaches/crosses the rebar yield strength (at ultimate strength considering DBE earthquake level) both in beam and slabs simultaneously as slab load is going to beam/columns. Therefore, it is realistic to assume same stiffness modifier of 0.35 for both slab and beams in case of two-way beam slab flooring system. Thus, underestimation of demands in beams is not understandable. (2) Crack control width may be checked at ultimate load, if it is OK at strength level, it will be automatically OK at service level. However, if you provide the cover and reinforcement spacing/diameter as per serviceability limit of code, then crack control width may not be an issue at the service level and ultimate level loads for given size of cross section and spans. (3) The concrete shall crack when its tensile strength exhausted and this will happen in most of the cases even well below the service level gravity loads, therefore it is hard to justify the modification factor of 1 especially for flexural members such as beams. (4) This is not clear how structural performance will improve if we design with modification factors of 1.0. The earthquake resistant design philosophy relies on ductility i.e.: plastic hinges are allowed at the base of the wall and columns and at the end of beams. The plastic hinges are not allowed in the columns. The modification factor of 1.0 will increase flexural strength of beams much more than the seismic flexural demand. This will not allow the beam to yield/development of plastic hinges in case of design level earthquake and there is pretty much chance of shifting the plastic hinge mechanism to the columns ends in several stories converting them to soft stories, drift concentration and failure.So, designing beams for modification factors of 1.0 in all members contradicts the earthquake resistant design philosophy and one need to reconsider the “R” factor for these cases to (a) avoid development of plastic hinges in columns (b) forces foundation. (Article is written with a fruitful discussion with my Senior Colleague Dr.Munir Ahmed,)

it depend on the project type(steel, concrete, building, bridge etc) and quantity of work. steel fabrication drawings are more time consuming and higher rates (fabrication draftsmen are less) while rcc structure shop drawings are comparatively less time consuming and have less charges. it can not be said the just drawings will cost 0.5-1% of project cost, it is possible for some projects, it is too much for just drafting of big projects.

it is good idea, even if limited ads for members is required to compensate the self supported forum site .

i confirmed this by making a model in SAP and load transferred, there was not any error. @Rana Rana sab please shed some light.

Dear Ilyas column will take load and without any issue, in SAP or ETABS we draw center-lines, so why column will not take load? Regards

yes you can assign load of pick up to beam.

Dear @muneeb1213 you have to consider loads on top of wall coming from the basement slab or any other wall directly on the wall. wall has basement slab attached on top so it will be like propped cantilever. there is an example 14.3 for basement wall(propped cantilever) in book "structural concrete by Nadim Hassoun" . you can design basement slab just like slab panel also if columns are closer and providing a beam at the top & bottom of wall and columns will act and must be designed as beams also but do check wall for shear against soil pressure at bottom half. Regards

Dear Abid please share your model and architectural plans, so that somebody could review it. one major reason is of assigning supports at all levels and second is oversize members(columns,beams) as uzair sab mentioned above, 3rd is shorter spans and equal loads going to columns. regards

i found another related discussion another document i found a somewhat good summary for modifiers https://www.academia.edu/13211701/Stiffness_Modifier Stiffness_Modifier.pdf

good comparison!! it means designing with modifiers will give more practical results and better moment redistribution. what is the effect of modifiers on lateral deflection?

Dear fellows! I have observed that some senior engineers have not been using stiffness modifiers in their designs. What is the concept behind i am not clear . As we design RC for strength, section is cracked and to cater for this cracked section, property modifiers are used as per ACI 318-11 10.10.4 (stiffness requirement) ACI 318-11 8.7 (stiffness requirement) UBC97 1630.1.2 (modelling requirement) so why whole section is considered in design. is there any other logic which i couldn't understand. Regards

as i scale the distance between the two footings it seems 2.00, it ensure the upper foundation load will not intersect the lower foundation directly(45 degrees rule), place the footing in steps as you described. if you are excavating by excavator it would be difficult to maintain the level during excavation, if it is manual excavation it will be feasible, provide tie beam it will improve the load distribution. these are my perceptions, i request to others please comment . regards

If there is difference in NSL on site change the foundation level as per NSL , Place your foundation at competent soil strata(hard soil, having no organic material or loose patches). you can make foundation in steps as well, go deeper for the depressed zone. there might be more appropriate answer if you share a sketch of your building and its foundation, contours etc. information of building will help to understand the problem more accurately. Regards

There is some material available which indicates that adding marble powder 10%-15% increases compressive strength and then it decreases.

Yes it is possible.

Dear friends what are the most critical load combinations(service and strength) for zone 2B please. Regards

Dear Umar there should be some exception of posting for some senior members who join the forum have less time but their input is invaluable. Regards

i applied a wind pressure of 30psf on one side of the pole and got 1.6M=40k-ft and shear 1.6V=1.76, m not sure about the factor 1.6. anchors are 12" apart at center.

Thanks Sir umar pole has 10 inches dia and base plate is 15in x 15in, with four anchors option on four sides. no loads for anchors are provided by manufacturer, an approx weight of pole is given 350Kgs mounted with 2x lights panels weight 80Kgs . wind speed 100mph for islamabad area. i am not clear if wind will be applied on one side of the pole (half area) or suction may also be applied. Regards

Salam Dear Sefpians!! I have to design a foundation for a 15m high floodlight pole, dia of the pole is 10 inches, pole is welded with the baseplate (provided by manufacturer), how the forces will be transferred to anchors. what forces will be on anchors. how forces will be transferred from anchors to foundation. anchors will be embedded in-situ concrete. Regards

i guess the one with beam will perform better than the simple foundation.

We may plan to have such obligations and bindings for engineering community, it may not be implemented for all at least we may start one for SEFP members.:-) Regards

Salam Dr.Amjad Saqib!!! I love this person for his efforts to reduce the poverty with dignity. Founder of Akhuwat Foundation speaks from his heart,wondefully . Listen to his speech at TEDx

Salam Dear Fellows In SEFP first ever meeting, it was discussed to register SEFP as PEB (Professional Engineering Body) affiliated with PEC to contribute to the engineering community positively and give CPD to registered members. We are here with some ideas and concepts in common like structural engineering and sharing. Hope you all would like this idea of registration. Rregistration/guidelines form is attached for reference to study and to discuss the process and willingness of the members. Regards RegistrationRenewal Form for PEB.doc