For a building, structure design phase is the most crucial phase of a project. After the paper work completion of feasibility analysis and architectural designing, it is the responsibility of structural design engineer to bring it to reality. After receiving all the inputs from architect, geotechnical engineers and clients, a structural engineer efforts to complete the picture that can be easily implemented on ground. A good engineer is one who manages his task without getting panic. Here are few steps that might help young engineers.
Define Project Description and Design Basis
The first step to the structural design process is describing the project, its objectives and design basis. Generally project description consist of project title, client/owner name, location of project etc. Objectives of the projects are defined at start i.e. scope of work, deliverable, schedule, roles of project teams etc. Structural design basis are defined at start of structural design process. The design basis consist of basic design parameter e.g. material properties, design codes, soil properties, wind and seismic profile of the area, loads and load combinations.
Detailed Review of Architectural Drawings
That might look trivial but this is the most important part. Each and every line work and notes have its significant. Some information is not clearly understood from plan. You need to review sections and elevations details to understand a sunk or sloped surface. Layers defined in AutoCAD file may help you understand material type and properties.
Comprehensive Study of Geotechnical Reports and Design Maps
Soil reports contain important information of sites e.g soil type, bearing capacity, soil moisture content, bore holes details, ground water table, SPT etc. It also gives site class and seismic details of the area. If any information is missing you can use USGS site to get details of the area. These maps will give you wind and seismic input for designing. These inputs will be the basis on which structural framing and foundation will be decided. Similar buildings in two different areas may require a totally different design strategy.
Documentation of Project
Take a pen and a paper with you while reviewing inputs. Make a project description list and note down all information in it. Make a project file and attached that page at first. Whenever you want to review the project and needed revision, you do not need to search here and there. That file will contain all calculations prints and hand sketches. You can also add contact list related to project and clients and contractor comments in this file with dates.
Developing Structural Scheme
Pick some color pens from bucket and mark the possible framing on the architecture drawings. Mark the possible locations of columns and walls. Try to make structural scheme regular by providing expansion joints, if building is irregular shaped. If there is some elevation difference, overhand or cantilever, sketch it to understand the supporting system. Workout minimum required sizes of structural members. Share these sketches with your architect to get reviewed before proceeding.
Various software packages are available for structural design of building. Most renowned software are ETABS, STAAD Pro., RISA 3D etc. For ETABS, structural design process is simply categorize is 3 steps. First define grid system of your model, second define material and section properties, third and last define all load cases and data you have gathered. Try to bring simplicity and symmetry in your framing. Once completed, run analysis to get drift and deformation values and compare it with allowable.
Sometime member sizes are sufficient for gravity loading but you need to increase sizes to resist lateral drifts. In column section defining, use CHECK REINFORCEMENT option instead of design. Provide a minimum 1% in all columns initially and check capacity. This will help you grouping out column sizes and reinforcement. If you have shear walls, mesh it first define piers and workout stresses and reinforcement. If required, you can add more walls. Make tables on Excel for Shear Walls and Columns. Check Base Reactions and workout footing. You can use software for footing and slab designing. Sketch everything and insert it in your project file.
There are number of software available for drawings. Widely used drafting software are AutoCAD and Microstation. Engineer can prepare drawings after designing and sizing the structural elements, but it is good practice to work parallel. Once your framing is final with required columns, beams and shear walls, draw it. Software modeling is based on center-line layout and center joints but in actual you have eccentricity in your framing. While making drawings you have to consider the soil profiles, alignments and levels of the ground.
Site Visits and Inspection
Engineer’s responsibility is not end by delivering design and drawings. Visit the site and see the implementation of your design. Explain your contractor if required. If a regular visit is not possible, ask your client to share site images and work progress. A good communication between stake holders is prime key for project success.