Steel Structures: From idea to Realization

Introduction

Steel Structures are the structures built up by structural steel sections. These steel sections are available in the market today in various specifications depending on the size, shape, unit weight, and many more distinctive characteristic properties to suit the diverse project requirements. The most common Structural steel types available in the market today are I Beam, Channel sections, Square or Rectangular Hollow sections, Angular sections, and Plate sections.

The different steel structures we witness across the globe have a particular structure type. Various types of steel structure buildings that exist are framed structures comprising beams and columns, grid structures comprising lattice and domes, truss structures comprising of bars or truss members, arch structures, arch bridges, prestressed structures, beam bridges, truss bridges comprising of trussed members, cable-stayed bridges and suspension bridges.

A structural steel building has a low value of weight to strength ratio, making it an efficient and cost-effective construction material.

The buildings which are tall or large in area benefit immensely from the speed of construction work. Industrial buildings and prefabricated buildings can be easily built in a cheaper way and can be repaired easily. Residential living spaces also benefit greatly from the property of structural steel sections, i.e., increased strength and durability. Structural steel is also seen to be highly advantageous for bridges due to its low weight and high strength.

Building design

First, a proper arrangement of columns/beams has to be made for an optimum design. The Construction should serve the basic purpose and need to have a pleasing look. Various things should be taken into account in the planning stage, like arrangements of rooms, ventilation, lighting, acoustics, etc. When the disposition of the building is made, the structural design process starts. It is crucial to understand the behavior of structural elements subjected to loads and to design them optimally, providing an economical and safe structure.

There are a few stages when designing a structure:

• Creating the disposition of the building

Position of columns and beams, spanning of slabs, stair layouts, choosing the type of footing.

• Define all loads and actions that act on the structure

All loads should be correctly calculated, including self-load, imposed load, wind and snow loads, seismic loads, etc, and then inserted into the calculation model.

• Analysis methods

There are three different methods currently used for structural steel design: simple design, continuous design, and semi-continuous design.

In the simple design of steel structures, all joints are considered to be pinned, which means that the bending moments developed are not transferred from one member to the other through the joints. Resistance to lateral loads such as wind forces and earthquake forces are provided by the structural steel bracings provided in between the frames of the building. In some cases, shear walls built of concrete serve as a core to protect the building from the destructive force of wind and earthquake.

In the continuous design of steel structures, all joints are assumed to be fixed, which means that the transfer of bending moments occurs from one member to the next member through the joint. The connections provided at the joint may vary depending on the design method, whether it is elastic or plastic. In elastic design, rotational stiffness must exist at joints and it must be able to carry the moments, forces, and shears in the structure. In plastic design, a tendency of formation of plastic hinges exists. The joints, in this case, must be designed and detailed for adequate rotations.

In the semi-continuous design of steel Structures, two methods exist in the design. In the wind moment method, beam joints and column joints are assumed to be pinned while considering gravity loads. On the other hand, while considering wind loads, the joints are assumed to be fixed.

• Design all the members

All members should be given an appropriate section that satisfies the deflection and strength criteria.

• Preparation of 3D model and workshop drawings and creating schedules

General arrangement drawings should be created as well as workshop and 3d installation drawings for the fabrication and installation of the structure.

Steel manufacturing

Structural steel manufacturing involves the process of producing steel from iron ore, predominantly. The whole process can be divided into three sub-processes.

In the primary stage of steel manufacture, the raw iron ore which is crushed and sorted is sent into a blast furnace from the top and heated. Hot air enters the furnace through the bottom. In this manner, iron is smelted into Steel.

In the secondary stage of steel manufacture, additional elements such as dissolved gases or alloying agents are added.

In the tertiary stage of steel manufacture, Steel is cast into rolls or sheets. Steel types such as beams, channels, angles, plates, and hollow steel tubes are the most common configurations of structural steel.

Steel fabrication

Structural steel sections are very malleable and can be modified into the desired shape of application by a skilled fabricator or welder.

Three common methods for connections exist riveting, bolting, and welding in order of their prevalence. Nowadays, welding is the most suitable and common method for fabricating Structural steel sections due to a couple of reasons: the resulting structure can be highly optimized in terms of weight, as compared to riveting, hence making the structures cost-effective,  and due to the ease to transport, mold, and set up at the site of construction.

Installation

The installation of Steel structures can be summarized in the following steps:

1. Setting the anchor bolts.

Anchor bolts are a key component of any structural framework. It helps hold the superstructure steadily on the ground.

2. Setting up the superstructure

The Structural steel members, fabricated at workshops are brought to the site and set up, one after the other, in accordance with the plan. Firstly, columns and rafters are placed. Later, the purlins, girts, braces (flange braces, wall braces, and roof braces) are aligned. In the next stage, fabrication and installation of roof panels and wall panels are completed. The gutters and downspouts are carefully laid. Trims and other necessary accessories must be laid before the structural steel building project ends.

Inspection

Inspection is necessary from time to time such that no inconsistencies occur during the election procedures. It is to be continually done, from the arrival of materials on-site to the final handover of the project to the client. The inspection shall be conducted on all Steel members such as rafters, purlins, columns, etc. Also, painting, connections, roofing, cladding, and other equipment must be inspected.

Members must be inspected for any damages during careless mishandling or storage. The positioning of fillers and washers for the connections needs to be ensured. The alignment of members must be checked at all times to ensure proper stability. All vertical and diagonal bracings in the structure must be tightened and in position. Roof and gutters must be cleared out of any debris or metal waste.

A final inspection of the structure must be done before the project is handed over to the client. All the bracings must be in position and tightened firmly. The bolts must be checked for their tension values and corrected to the exact value. Any screws left improperly must be drilled firmly. Damaged paint at any specific area must be given a touch-up.

Reference:

1. https://en.m.wikipedia.org/wiki/Steelmaking
2. https://theconstructor.org/structural-engg/methods-of-steel-structure-design/6876/?
3. amp=1https://methodstatementhq.com/steel-structure-building-construction-procedure.html
4. https://www.directorsteelstructure.com/steel-structure-building/

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