STEEL CONSTRUCTION
Steel Material
Steel is an alloy of ferrous metal as a basic element with several other elements, including carbon. Steel material has advantages compared to other materials, namely wood that is easily weathered, stone that requires large volumes, or concrete that lacks tensile strength and is too brittle to bend. Besides its great strength to withstand tensile and compressive loads without requiring a lot of volume, steel also has other very beneficial properties that make steel one of the most common building materials used today. Steel to be used in the structure can be classified into carbon steel, high strength low alloy steel, and alloy steel. Steel classifications include:
- Carbon Steel
Carbon steel is divided into three categories depending on the percentage of carbon content, namely: low carbon steel (C=0.03-0.035%), medium carbon steel (C=0.35-0.50%), and high carbon steel (C= 0.55-1.70%). Steel that is often used in structures is medium carbon steel, for example BJ 37 steel. The carbon content of medium steel varies from 0.25-0.29% depending on thickness. In addition to carbon, other elements that are also found in carbon steel are manganese (0.25-1.50%), silicon (0.25-0.30%), phosphorus (maximum 0.04%) and sulfur (0.05%). %). - High Grade Low Alloy Steel
Which is included in the category of high-strength low-alloy steel has a yield stress in the range of 290-550 Mpa with a breaking stress (fu) between 415-700 Mpa. The addition of small amounts of alloying materials such as chronium, columbium, manganese, molybdenum, nickel, phosphorus, vanadium or zirconium can improve the mechanical properties. If carbon steel gains strength along with the addition of a percentage of carbon, then these alloying materials are able to improve the mechanical properties of steel by forming microstructures in finer steel materials. - Alloy Steel
Low alloy steels can be tempered and heated to obtain a yield stress of between 550-760 MPa. The yield stress of alloy steel is usually defined as the stress that occurs when a permanent strain of 0.2% develops, or it can be defined as the stress when it reaches 0.5%.
Steel Advantage
Conventionally, people often use wood for building construction, such as building bridges and so on. Unfortunately in the development of time, the need for wood is considered less than ideal, especially in terms of environmental friendliness. The use of steel construction makes the problem solved easily. Especially for the need for a solid building foundation. This product can improve the weakness of similar functions that people have been using wood for a long time. Here are the advantages of Steel Construction that we can get for the foundation needs of a building:
- High Strength
Nowadays, steel can be produced with various strengths which can be expressed by the yield compressive strength Fy or by the ultimate tensile stress Fu. Although steel is of the lowest strength type, it still has a higher strength-per-volume ratio when compared to other commonly used building materials. This allows the design of a steel construction to have a lower dead load for a longer span, thereby providing the excess space and volume that can be utilized due to the slender profiles carried. - Ease of Installation
All parts of steel construction can be prepared in a steel workshop or factory, so that when workers arrive in the field, all they have to do is install the prepared construction parts. Most of the construction components have standard shapes that can be obtained at iron shops so that the time needed to make existing steel construction parts can be done easily because steel components usually have standard shapes and certain properties, and easy to get everywhere. - Uniformity
The properties of steel, both as a building material and in the form of a structure are very good, so that the elements of steel construction can be carried out in accordance with those in the plan. In this way, the process of waste that usually occurs in planning can be avoided. - Ductility
The property of steel that can undergo large deformations under the influence of high tensile stresses without breaking or breaking is called ductility. The existence of these properties makes the steel structure able to prevent the sudden collapse of the building. This property is very beneficial in terms of the safety of the building occupants in the event of a sudden shock such as an earthquake.
Mechanical Properties of Steel
According to SNI 03-1729-2002 concerning Procedures for Planning Steel Structures for Buildings, the mechanical properties of structural steel used in planning must meet the minimum requirements given in the table below. The yield stress should not exceed the given value. The breaking stress for design (fu) shall not be taken beyond the values given in the table. In the design of steel structures, SNI 03-1729-2002 takes several mechanical properties of the same steel material, namely:
- Modulus of Elasticity, E = 200,000 Mpa
- Shear Modulus, G = 80,000 Mpa
- Poisso number = 0.30 Mpa
- Coefficient of long expansion, = 12.10 -6/0C
| No | Steel Type | Minimum Breaking Voltage, fy (Mpa) | Minimum Yield Stress, fy (Mpa) | Minimum Stretch (%) |
|---|---|---|---|---|
| 1 | BJ 34 | 340 | 210 | 22 |
| 2 | BJ 37 | 370 | 240 | 20 |
| 3 | BJ 41 | 410 | 250 | 18 |
| 4 | BJ 50 | 500 | 290 | 16 |
| 5 | BJ 55 | 550 | 410 | 13 |
P = Load
A = Cross-sectional area
ΞπΏπ = Elongation or change in length between two reference points on a tensile specimen
πΏπ = original length between two reference points on the tensile specimen before loading
Structural Planning
Structural planning can be defined as a mixture of art and science combined with a structural engineer's intuition about the behavior of structures with basic knowledge in statics, dynamics, mechanics of materials, and structural analysis, to produce a structure that is economical and safe throughout its service life.
The purpose of structural planning according to the Procedures for Planning Steel Structures for Buildings (SNI 03-1729-2002) is to produce a structure that is stable, strong enough, serviceable, durable, and fulfills other purposes such as overturning, tilting, or sliding during the design life of the building. The risk of structural failure and loss of serviceability during its design life must also be minimized within acceptable limits. A durable structure should not require excessive maintenance costs over its service life. Planning is a process to get an optimum result. A structure is said to be optimum if it meets the following criteria:
- Minimum cost
- Minimum Weight
- Minimum construction time
- Minimum labor
- Minimum manufacturing cost
- Maximum benefits during service
The structural planning framework is the selection of the arrangement and size of the structural elements so that the working load can be carried safely, and the displacement that occurs is still within the required limits. One of the important stages in planning a building structure is the selection of the type of material to be used. The types of materials that have been known in the construction world include steel, reinforced concrete, and wood. Steel material as a construction material has been used for a long time considering its several advantages over other materials.
Steel Profile Types
The following are the main types of steel profiles commonly used in Indonesia as building materials for various constructions as needed.
- Wide Flange (WF)
- Chanel U atau UNP (Kanal U)
- Lipped Channel/C Chanel/Kanal C (CNP )
- T-Beam (Hot Rolled)
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