Theory and design of Structures

FRAME2Dexpress is a program for static and dynamic analysis of 2-dimensional framed structures. Distributed or nodal dead and live loads can be specified. Load combination is used according to Eurocode 1, with user defined load combination coefficients. The program performs computation of internal forces and diagrams for displacements, bending moments, shear and axial forces. In the dynamic analysis the eigenfrequencies and the mode shapes are computed. Graphical output for the diagrams and mode shapes is displayed.

Although the software[Ectools] has the above mentioned capabilities, only the flexural design of 1D elements, 2D walls and cores feature is available[free]. In simple words one can use the software to check the capacity of a given wall sections...I.e, we use it to check the flexural strengh of shear walls.

ECtools© is a design software for Reinforced Concrete and Unreinforced Masonry Structures using either the European Norms (Eurocodes) or the ACI318-11& ASCE/SEI7-10 US norms. It to facilitate the practicing structural engineer or the design office in the correct application of the several clauses of these codes. It utilises the analysis results of either SCIA Engineer© or-for the Eurocodes- ETABS© and can be used in the following cases: √ Seismic design of Reinforced Concrete Buildings √ Checking/Reviewing the Design of Reinforced Concrete Buildings √ Seismic Assessment and Retrofitting of existing Reinforced Concrete Buildings √ Seismic design of Composite buildings with Concrete Cores (The cores) √ Seismic design of Unreinforced Masonry Buildings √ Seismic Assessment and Retrofitting of existing Unreinforced Masonry Buildings √ Preparation of the static inelastic analysis model according to the  procedures of the Eurocodes and  FEMA. KEY FEATURES ECtools has some key features which when beeing combined render it one of the most efficient design tools in the European Market: √ General Building Checks fitting the requirements of EN1998 or ACI318-11&ASCE/SEI 7-10, such as: • Automatic definition of building type • Automatic calculation of behaviour factor q • Torsional Sensitivity • P-D effects • Required seismic joint at each level √ Application of the capacity design concept which is inhrent in all modern seismic codes • Capacity design of joints (the weak beam - strong column rule) • Capacity shear design of all members for ductile behaviour (capacity shear forces) √ Flexural design of all 1D elements 2D walls and cores with biaxial Moment -Axial force interaction, utilising a very efficient algorithm that produces fast results, while applying the cracked sections design concept with parabolic stress distribution for concrete. √ Checking the design of a new building Input of the design results to be checked via excel spreadsheets Use of custom safery factors Indication of elements with inadequacy using red indictors in the status bar √ Seismic Assessment and Strengthenning of existing buildings Input of the design results to be checked via excel spreadsheets Use of custom safety factors for verified materials Use of element ductility factors (primary & secondary elements) Available stregthenning options with R/C jackets of existing elements Indication of elements with inadequacy using red indicators in the status bar.

An integrated and comprehensible software including all the structural Eurocodes. It is a work and studying companion for all the Eurocodes, from Eurocode 0 to Eurocode 8.  Eurocode 0, Basis of structural design Eurocode 1, Actions on structures Eurocode 2, Design of concrete structures Eurocode 3, Design of steel structures Eurocode 4, Design of composite steel and concrete structures                                    Eurocode 5, Design of timber structures Eurocode 6, Design of masonry structures Eurocode 7, Geotechnical design Eurocode 8, Design of structures for earthquake resistance  A complete package, and source of information on designing and understanding the Eurocodes, and the National Annexes. The program is buildt up from groups of components based on the structural Eurocodes. You can design structural object based on the different eurocodes, select National Annexes, adjust parameters, and do design and analysis of frame 2D-structures. Design charts and graphs for use and understanding the Eurocodes are included.   A detailed design report is produced for the designed structural components. Assumptions, graphics, references to the Eurocodes and the National Annexes are shown in the report. The user can select the applicable National Annex. Design code parameters, material values and default values can be adjusted. @theoryanddesignofstructures

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If u want to see how to apply stiffness modifiers to frame elements, please use the link below. It will lead u to a previous post in this channel. @theoryanddesignofstructures https://t.me/theoryanddesignofstructures/280

​​Stiffness modifiers as per ES EN 1998:2015 when applied to structural walls( such as ductile or large lightly reinforced concrete walls) is a bit different from how we do it for frames. In order to reduce the bending stiffness of wall in a given direction f11 or f22 should be modified as per the orientation of the local axes. At first glance f11 and f22 seems to modify the axial stiffness of the wall. Some might even argue m11, 22 and m12 should be modified in order to reduce the bending stiffness of the wall. This argument is wrong since m11, m22 and m12 modifiers are related to out of plane bending. And out of plane bending moments are usually negelect in order to reduce the amount of rebar required. The picture attached to this post shows how stiffness modifier for walls shall be applied. As can be seen from the picture the m11, m22 and m12 modifiers are set to be 0.1 in order to underestimate the effect of out of plane bending while trying to avoid numerical instability. @theoryanddesignofstructures

For further discussion of what is posted in the channel please join our group and post your questions. 👉 @theoryanddesign the link to the group.

Some of the steps to check excess points out of the frame which are often the causes of warning are (borrowed from Anjali, Civil Engineer, Quora): [Applies to CSI ETABS and SAP] Warnings like ' points to close' are due to geometrical errors in model & its gives warnings in directions are ux, uy & uz. These warnings can be ignored. Warnings like 'load not transferred' are the ones to be resolved always. These warnings mostly are due to improper meshing. If auto mesh is applied to membrane object or if it is not applied to shell object these warnings occur. It also for improper support condition, like for ex. If cantilevered beam is provided with hinged end support in model. These kinds of warnings cause non generation of modes. They are generally denoted in Rx & tu directions. Also check the Young's modulus E value in applied to building material, loads applied. Sometimes changing unit unknowingly may result in excessively high or low stiffness of the member, or load values may be incorrect. Also check member sizes. Most important: Always work in a single system of units. After checking these points check for unnecessary objects modelled. Go to selection dialog & keep visibility of points only. (IT IS IMPORTANT TO TURN OFF VISIBILITY OF ALL OTHER MEMBERS)Select all the points by dragging pointers in 3D view, make sure to select all the points. Check the no. of points selected on the ribbon below.Delete the points & recheck the no. Of points in the model. All the points that are not connected to the frame or shell members will be gone. Take care of the points drawn on any member to apply external force are not deleted. Bring back normal visibility of the frame & check model for warnings. If there are still warnings, run the model. After run is successfully completed, check whether modes are generated or not, if not select all slab/walls assigned with shell property & provide auto mesh to it. Also check in 3d space for disconnected null lines, ramps drawn accidentally. Apply end releases wherever hinged connections are required but are modelled as continuous due to geometrical requirements Now go to the tables & open the table showing defection i.e. table 'point displacement'. Check the deflection in vertical loads for any abnormality. Then check for lateral loads only. If there occurs any odd value at some point check that point, it's a culprit. Generally lateral load deflection limit is around .25H to .5H (H is the height of the structure) Also check lateral drifts in x &y directions. It shouldn't be more than 0.004 (as per IS code) Study Bending Moment & Shear Force diagram for vertical loads & horizontal forces separately in plan & elevations to check whether desired profiles are obtained. Always remember to basics of structural mechanics & cross check the software output. @theoryanddesignofstructures

VIS Concrete Design Software was developed by CSI Italia, with the intent of expanding SAP2000, ETABS and CSiBridge design capabilities to meet specific Eurocode requirements. Development of VIS started in 2004 and continues through these days, striving to make the CSI programs ever more suited for use in the European market. VIS provides you with a unique approach that intuitively follows the natural workflow used by structural engineers in their design process. Initially, you’ll be working on the model. This is done using one of the CSi programs. They are some of the most well-known and appreciated structural engineering packages on the market. You can use many VIS tools to help during the modeling phase. Including; Combinator that will automatically generate load combinations. Section Cutter that aids in the modelling of concrete walls. And, SPF that will let you explore seismic performance. Everything takes place within a single interface in the main software program (SAP2000, ETABS or CSi Bridge). VIS is fully integrated. This means VIS acts as part of the main program itself. And, permits you to move flawlessly back and forth; interacting with the model and exchanging data with it. Once satisfied with the model, you can run the analysis and take advantage of the limitless capabilities of the CSi software. You can check results, use design utilities, edit the model on the fly and redo the analysis until satisfied with the size of your concrete members. You decide which of these members you want to design in detail. You can select a few, or the entire model. Open the "Tool” menu and click VIS to enter the design session. Once the design parameters are set to your requirements VIS will automatically populate the entire structure with preliminary reinforcing. Not just required areas. But, fully detailed longitudinal and transverse reinforcing. This reinforcing meets all code requirements but will probably be a long way from your desired results. It is a very helpful starting point, though. From there you can use the powerful editing and design capabilities in VIS to revise the reinforcing to way you want it. And, tailor it exactly to your project needs. Once finished, you can take advantage of the many output features and then transfer the results to calculation reports and working drawings. 👇🏽👇🏽👇🏽 @theoryanddesignofstructures

PRESTRESSED CONCRETE FINAL PART Tendon Layout Tendons can have the following type of arrangement on plan 1. Distributed - distributed (common in MIddle east and Australia) Tendons in the x and y directions are distributed over the length of the slab with a spacing not exceeding 1.5m. The issue with this arrangement is the tendon will be like a basket wieve and it’s difficult to know which one goes up and which one goes down. 2. Banded - distributed (common in US) This will have the same distributed tendon as part 1 but one direction will be banded (usually grouped in a width 1-1.2m). No max spacing requirements for banded tendons Very easy to install as all the banded will be install first then the distributed 3. Banded - banded Not very common Note: the horizontal spacing between tendons doesn’t affect the structures a lot, the most important thing is the tendon profiles (measured vertically) Economy of PT system PT slabs will commonly have up-to 30% less thickness, and complete flat plates. The deflection and cracks are significantly reduced as we are allowed to use the full E in the calculation of deflections (both short and long term) Note: I have noticed many engineers and consulting offices in Ethiopia ignore to check the long term deflections, this is a wrong practice, and not allowed by any code I know. Some engineers might argue saying ‘well we have done this and that without long term and the building is ok’ this is all what I have to say for that, your building is ok for the short term you can’t see the long term effect in short term. The other significant saving related to PT is rebar, even though practically (code accepted) we can make a slab without any bottom rebar it is common to use a very light mesh (T10@500mm or even more) for bottom mesh as integrity bar. With PT one can save a significantly high rebar, up to 70% saving in rebar is very common. Cost comparison The cost comparison listed below are based on real projects in Ethiopia where I have done the design comparison The prices include the design, material and installation costs of PT, rebar, concrete and formwork PT vs Flat slab A cost saving of 540birr/m2 can be achieved with post tensioning. For a B+G+12 building with a floor area of 800m2, a direct saving of over 6million can be achieved only from slabs. More saving can be gain from foundation size (even more if mat PT is used), from speed of construction etc PT Vs Beam - slab Here I should begin by saying this, based on my assessment and some other engineers. We have not found any cost saving by Beam - slab system against rc flat sla. So the saving will be the same as the flat slab, even more saving in time and formwork will be there as well. The aesthetics of the two systems is also incomparable PT vs Ribbed For this comparison i only took a ribbed slab design from a consulting office ( I have not made any design check), and did the quantities my self. Surprisingly enough this system consumes more rebar and only saves a little bit on the concrete, but costs more on formwork. So based on the quantities a saving of more than 570birr/m2 was calculated. So for the same project size one can save more than 6.4million birr. Thanks for you attention, any questions are welcome

PRESTRESSED CONCRETE PART 5 Myth associated with PT - we cannot make an opening in PT slab, this is actually a false statement, a PT slab can be modified with proper calculations and expertise. We have made as big as 4m x5m opening in a PT slab which was required for sky light or escalators - we need to do restressing periodically: this is also one of the things I hear about PT, but this is wrong. The strands are cut flush with the concrete surface and can not be restressed even if we wanted to. There is no requirements for restressing as we have low relaxation strands and a very good wedge anchor system - PT slab can not crack: even though PT slabs are designed to be crack free at service load (at least based on ACI, some codes like EC allow for a certain degree of crack), cracks can be witnessed in PT slabs. This can attribute to one of the two 1. If the actual load exceeds the service load momentary 2. Surface cracks, which are very common No one can claim to have a crack free concrete by definition, we will still have micro cracks Design based on ACI Vs Euro Code - The analysis procedure and the load combinations are similar for the two codes. - ACI restricts the tensile stress at any time and section to be way below the cracking moment. While EC allows those limits to be exceeded to some extent, but then gives min rebar requirement to supplement that - Both codes do not have any min rebar requirement for positive moments (bottom) in bonded PT, this means one can design a PT slab with no bottom rebar - Further more; ACI has no top or bottom min rebar requirements for bonded PT slabs up until the 2011 code, so with ACI 2011 or earlier code, one can design a PT slab with no rebar - if a slab is designed with ACI, we will get more PT and less rebar than slabs designed with EC. Any questions are welcome

PRESTRESSED CONCRETE PART 4 Definition of terms Strand: is the high tension cable (typically more than 4 times the strength of rebar) Tendon: agroup of strands (can be one for unbonded but it’s multiple strands inside a duct for bonded system) Duct: a galvanized or HDPE that separates the concrete from the strand Issues associated with PT - Restrain to shortening: this needs a special consideration for pouring sequence and connection detailing - Relaxation of strand: this can be avoided with a use of low relaxation strands Design of Post tension members The design of post tension elements needs a sound engineering knowledge and field skill, the amount of force applied to a single strand with a diameter of 12.7mm is about 15Ton (this is more than the weight of 7 Toyota Corollas). One can imagine how dangerous it can get if either the design or site execution are not properly done. That’s why all countries (at least the countries I am aware of) requires a specialized contractor who can do the design, execute the job and take the liability; no consulting office, no mater how big they are, are not allowed to do a PT design (this actually goes to structural steel, pile, shoring ... as well) The design of PT elements involve three steps: these are load balancing (equivalent load), service design and ultimate load design. Even though PT was developed more than a century ago and has been on practice for over 70years, only few schools teach the subject either in US or Europe. That can be attributed the amount of work require to reach to a safe, and economical design, what I mean by that is two engineers can have completely deferent designs results for a simple beam or slab. For example, if a person calculates a required steel beam size of 305x127x42 but decide to use a size 356x171x45, that beam memeber is still safe, even though it might not be the most economical. But in case of PT, a beam with 12 strands can be safe but the same beam with 20 strand might not be safe. In short term more strand does not mean safe, that makes the design of any pt members trickier and as for me enjoyable

Multi strand system