The modelling process

I would recommend this book to every structural engineer. Very easy, precise and concise. I have developed a flow chart and a short summary out of the chapters related to modelling process.

The process discussed here is advocated in IstructE (2002), MacLeod (1995), NAFEMS (1995, 1999) and ISO 9001 (2000). It tends to be used in a formal way by those who specialise in analysis modelling.

By formal is meant that a written record of the activities always be adopted in order to reduce risk in analysis modeling.

The degree of understanding gained from doing hand calculations is normally overestimated. Reflective consideration of results is a more fruitful source of understanding than arithmetical processing. Engineers were concerned that the introduction of computers would result in dumbing down of engineering. ‘Monekys’ could be trained to hit the right keys. While there is a significant danger that software can be used in the absence of competence, the reality of computer use for modelling is that it has made the work more intellectually challenging.

To operate successfully in environments of significant uncertainty requires intellectual power of the highest order. This is the realm of modern structural analysis – the realm of the professional engineer.

Risk is defined as the combination of the likelihood and the consequences of an event which can cause harm. The likelihood of occurrence of a disaster due to structural analysis modeling is low but the potential consequences from such an event are severe. The risk of a disaster causing serious harm due to inadequate modelling cannot be eliminated; it can only be minimised. But to be minimised, the modelling process needs to be formally adopted.

There are two basic processes in structural analysis;

1-Model development process

2-Solution process

Traditionally, the model development process was a minor issue but today, the emphasis for the structural engineer has changed radically from analysis to model development. The paradigm shift has not been identified in education and hence it is not well understood in practice. Following tables gives the comparisons between the skills needed in practice and skill given in education.abilitiesModelling process (as explained in theory and in the given flow chart) can be interpreted as implying a linear implementation, the real process is likely to involve much looping back to previous stages.

Download the flow chart

3 Comments

  1. Excellent topic. There are two types of engineers. One who claim that they are good in theoretical approaches and there are others who think they are expert in computer applications. To judge who is perfect we must check their work and their reviewer feedbacks.

    In reality computer applications have camouflaged many engineers incapabilities and lack of engineering knowledge. In my opinion to check who got the real talent, is by looking into how much he is actively he is participating in different engineering forums discussing and sharing technical knowledge based issues. Also if someone has real guts and potential he have passed difficult testing programs such as Istruct or NCEESs’ PE or SE or Dubai Municipality test etc. Today softwares and engineering spread sheets are excellent tools used by fake and incompetent professionals to hide their inefficiencies.

    Best regards

  2. I was wondering if you can help me with this?
    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 6.5×0.25(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 you clarify me on how to design a building with soft story in etabs?

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