INTRODUCTION TO STEEL DESIGN

Steel is widely used as a building material. This is because of a number of factors including its mechanical properties, availability in a variety of useful and practical shapes, economy, design simplicity, and ease and speed of construction.Steel can be produced with a variety of properties to suit different requirements. The principle requirements are strength, ductility, weldability, and corrosion resistance. Recently, mild steel was the most common material for hot-rolled shapes but has now been superceded by higher strength steels for a number of shapes.

STRESS-STRAIN CURVE OF STEEL

The figure on the left shows the stress-strain curves for ASTM A36 mild steel and a typical high strength steel.
From the curve, it can be seen that loading and unloading a mild steel specimen within the elastic range produces no permanent deformation and the specimen returns to its original length after unloading.
The yield point is followed by plastic yielding with a large increase in strain occurring at a constant stress.The increase in strain during plastic yielding may be as much as 2 percent.
The stress-strain curve for high-strength steel does not exhibit a pronounced yield point. After the elastic limit is reached, the increase in stress gradually decreases until the tensile strength is reached. For these steels a nominal yield stress is defined as the stress that produces a permanent strain of 0.2 percent

The stress-strain curve for mild steel indicates an initial elastic range, with stress proportional to strain, until the yield point is reached at a stress of 36 ksi. The slope of the stress-strain curve, up to this point, is termed the modulus of elasticity and is given by the equation shown on the right.

steel shapes

The dimensions, weights, and properties of these sections are given by American Institute of Steel Construction, Steel Construction Manual (AISC Manual)1 Part 1.

The types of steel available for each structural shape are summarized in the table as shown in the right. Its corresponding specified minimum yield stress and tensile strength were also provided in the table.

steel building types

Steel buildings are generally framed structures and range from simple one-story buildings to multistory structures.
Steel buildings may be constructed with steel roof truss or open web joists or using single bay rigid fame structure. Framed structures consist of floor and floor diaphragms, beams, girders, and columns

BEAM DETAIL

GIRDER DETAIL

COLUMN DETAIL

As well as supporting gravity loads, framed structures must also be designed to resist lateral loads caused by wind or earthquake. Several techniques are used to provide lateral resistance including special moment-resisting frames, braced frames, and shear walls.
Moment-resisting frames resist lateral loads by means of special flexural connections between the columns and beams.Moment-resisting frames have the advantage of providing bays free from obstructions.
Shown in the left are concentrically braced and eccentrically braced frames which possess the advantage over moment-resisting frames of less drift and simpler connections.

building codes and design criteria

The building code adopted by most jurisdictions throughout the Philippines is the National Structural Code of the Philippines (NSCP). In addition, two specifications for American Institute of Steel Construction can be used. These are Specification for Structural Steel Buildings (AISC 360)8 and Seismic Provisions for Structural Steel Buildings (AISC 341).9 The Specification for Structural Steel Buildings is included in AISC Manual Part 16. The Seismic Provisions for Structural Steel Buildings is included in AISC Seismic Design Manual (AISCSDM)10 Part 6. The Specification and the Provisions provide complete information for the design of buildings.
AISC 360 provides criteria for the design, fabrication, and erection of structural steel buildings and structures similar to buildings
Attached below is a copy of AISC Manual 14th edition. This can be used for checking the dimensions and properties of structural products in various shapes that is used for steel building design and construction.

AISC steel construction.pdf

asd and lrfd concepts

The allowable stress design method specified that stresses produced in a structure by the working loads must not exceed a specified allowable stress. The allowable stress, also known as working stress, was determined by dividing the yield stress of the material by an appropriate factor of safety.
In 1986, American Institute of Steel Construction introduced the load and resistance factor design (LRFD) method. In this method, the working loads are factored before being applied to the structure.The design strength, is determined by multiplying the nominal strength of the member by an appropriate resistance factor.
Shown in the left are the relations between the required strength and the allowable and design strength multiplied by factor of safety and resistance factor, respectively.

supplementary materials and recorded meetings

rtp-tcyf-ibq (2022-09-21 19:10 GMT+8)

vur-jgcm-emb (2022-09-08 18:36 GMT+8)

20220908 - CENG131 Module 1.pdf

reflection:

After reading Module 1, I have learned and grasped so many takeaways even after our first and second session meetings. First is that in this subject, we can use both ASD and LRFD concepts for steel analysis and design. Unlike in the Reinforced Concrete subject, we only focused on using LRFD, due to its conservativeness and because it is considered a reliability-based design, which results in a more efficient design of reinforced concrete. In addition, I learned that girders and beams have differences, and every steel shapes possesses unique properties and dimensions, and that is why it serves a specific purpose when used as a structural steel material. Also, I have learned about the differences between concentrically and eccentrically braced frames, and the stress-strain curves between mild steel and high strength steel. It can be discerned from the figure that high strength steel does not really exhibit yield point. And for mild steel, it can be seen that plastic yielding occurs with a large increase in strain while at constant applied stress. Understanding these concepts is highly beneficial for me, since I can use it for analysis and design of steel structures in my future profession as structural engineer. In order to attain those, I should master the basic concepts first.

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