Month: April 2020

Steel Galvanization

Construction Galvanized Steel.

The zinc Coating when intact, prevent corrosive substances from reaching the underlying steel or iron. Zinc Coating is more durable coating for the construction site for protects the steel from the rusting effect. Zinc protects the steel by corroding it first. In the event the underlying metal becomes expose, protection can continue as long as there is zinc close enough to be electrically couple. After all of the zinc in the immediate area is consume, localize corrosion of the base metal can occur. Hot Dip coating in zinc coating is widely is use for the coating of iron and steel product,  because zinc coating is of thick and gets easily detachable with the iron rod due to its sticky material.

This is the most common use for galvanize metal, and hundreds of thousands of tons of steel products are galvanize annually worldwide. In develope countries most larger cities have several galvanizing factories, and many items of steel manufacture are galvanize for protection. Typically these include: street furniture, building frameworks, balconies, varandah, staircases, ladders, walkways, and more. Hot dip galvanize steel is also used for making steel frames as a basic construction material for steel frame buildings.

       Construction galvanize steel is mostly used as it is more durable and cost the galvanize zinc coating is also affordable for the the construction site.

Why To Use Zinc Coating?

 Without protection, steel will rust due to atmospheric conditions over time. The degree of rust will depend on the environment that the product is in. Rust is an iron oxide (typically a red oxide) which is formed by the reduction and oxidation reaction of iron and oxygen, in the presence of water or air moisture.

 Rusting of iron will increase if the Zinc coat is on perfectly attachable with the steel or iron product and due to which the bonding of weldment and steel does not occur and structure may eventually fail. 

Structure Detailing Process

Structure Detailing Process

Detailing of steel structures is a very critical process which requires high concentration and understanding. It is not a one day work. The other process of fabrication and erection depend on the detailed sheets completely and that is why any mistake can result into re-fabrication of component which is generally costly in nature because of Steel costs thousands more per tonne. 

After the design part is done a model is created with the help of software”s. In detailing each and every element is detailed with its height, width, shape, exact cutting length, cross section, connecting bolts diameter, welding and weldment assembly. Such a drawing is called a shop drawing, or a fabrication drawing, or manufacturing drawing. In the past these drawings were prepared by expert draftsman that use to consume a lot of time but now modeling software produces these drawings. If we talk about modeling software one of which is autodesk’s advance steel which comes with variety of drawing style applicable to any model thus saving time.

 

Types Of Drawings

a) Shop drawing                              b) Erection drawing

In shop drawings or detail drawings every minute detail of individual element or component (column, beam, braces, type and size of bolts, type and size of welding, etc) that needs to be made by the steel fabricator is mention. These include material specification, size, cross section, dimension, and number of times they are present. Also a complete bill of materials is there which gives an idea about how much cost would be incur. Erection drawings as the name suggest are helps in placing the elements in their correct position. These covers ground level heights, dimensions and position of each component, their connection details like bolt assembly, welding spots

The production of fabricated steel starts with the steel detailing group, which follows an established procedure to ensure an orderly flow of work through the shop. A tremendous amount of paperwork is involved. Drawings and bills (standard forms) prepared by the steel detailer form an important part of this paperwork. A steel detailer plays a tremendous role in the overall project progress. The detailer must be familiar with regulations and guidelines from all aspects of construction. OSHA, AISC, minimum

bearing limits, and common standards/practices must be included in the detailer& skill set. A good detailer can make even the most complex project very feasible for any fabricator. The drawing layouts prepared by the detailer must be understandable as it is not only seen by fabricators but are helpful for HVAC, plumbing installation perspective. Structural steel detailing process acts as a medium between the designer, architect and fabricator, any discrepancies in the drawing observed by the fabricator can directly or indirectly get resolved by bringing to the attention of the design team.

Detailing Procedure

typical detailing group would perform its procedures in approximately the following sequence:

  • • Initiate job and fabricator setup (i.e., pre-planned checklists).
    • Prepare typical details, job standard sheets, layouts, and calculation sheets.
    • Prepare system of assembling and shipping piece marks.
    • Prepare and check advance bills for ordering material.
    • Make and check anchor rod/embedment drawings.
    • Make and check erection drawings.
    • Make and check detail shop drawings, including bills of material.
    • Secure approval of shop drawings Incorporate approval comments.
    • Issue shop drawings to the shop.
    • Prepare lists of field fasteners.
    • Fit check.
    • Issue shop and erection drawings to field.

Maintenance of steel structure

Maintenance of steel structure

Everything in this world requires maintenance in order to function properly and effectively, whether it is a living or non living thing. Maintenance is very important as it determines the state of working and useful life conditions of any material. For ex. if you want to improve your health you do exercise likewise steel structures also need exercises of regular inspections. Things do change if regular maintenance is not done because steel structures are very much open to atmosphere and when it get contacted with atmospheric agencies such as moisture rusting can happen. The continuous oxidation of the surface of the structure result in their corrosion.

Off shore structures or marine steel structures ex. oil and natural gas, dockyards, etc need regular maintenance because of the presence of salt in the atmosphere. Reversal of temperatures also affects the durability of structure, you can imagine the state of steel structure in countries like UAE where the maximum temp rises to 50°C and countries like UK where the lowest temp record is -27.2°C. Steel structures also reflect the effects of temperature but these are not recognizable easily as in human beings. Therefore the structures are constructed according to the pertaining condition of its surroundings. You can’t apply the same condition in UAE that you have applied while constructing the structure in UK.

Types Of maintenance

Connection maintenace

  •  Corrosion checks
     Welding erosion
     Loosening of bolts
     Cracks in paint
     Minor hole
  •  
  •  
  • Following are the type of defects found in steel structures,
  •  Hole
     Crack
     Sliced border
     Corrosion.

Following are the type of defects found in steel structures,

  •  Hole
     Crack
     Sliced border
     Corrosion

While in marine structures you will find these defects mostly common,

  •  Contamination
     Deformation
     Deterioration
     Discontinuity
     Displacement
     Loss of material/ Erosion.

Causes

The offshore/marine steel structures gets affected the most because of their continuous contact with saline water that is why in most of the cases we use concrete structure but these also get susceptible to marine atmospheric agencies and causes efflorescence etc. The effect of atmospheric conditions on both concrete and steel varies greatly.

 One can see the changes frequently taking place on concrete structures such as discoloration, cracks, holes, mold formation due to moisture etc but it is very difficult to recognize the defect in steel structure because most of the defects goes unnoticed by even a common person also. It is highly difficult for an inspection team to detect every defect and repair them, some are present at inaccessible areas making it more difficult but thanks to advance technologies through which we can detect them but repairing them is still a challenge. 

The most common defect of steel structure is corrosion but have you ever seen it happening ,of course not because it’s a very slow process. When the steel comes in contact with moisture the rusting process starts which ends up with corrosion. If these things are not taken proper care then can result into deterioration of the structure which eventually can lead to other factors such as failure of joints, members or even structure, this means the waste of time and money which was invested to construct it.

Bolted Connection

Bolted connection

Bolted Connections

Bolted connection

Steel structures are incomplete without connections they indeed play an important role in steel structure formation. Unlike concrete structures steel connections are properly designed affirming to respective codes. Connections also become necessary when a certain length of member is needed to be
connected with the succeeding member because of limitations in available length.

Hence here come a nut and bolt connections. We have seen bolted connections in various steel structures, but have you ever imagine why they are so different in pattern, sizes, and the way they are assemble. All these questions account for the variations that we have in our connections. Let’s talk about dishes in which we have many recipes you choose one which makes the dish delicious similarly out of the many connections we have to take the desire one which confronts the design constraints and gives strength to the connection. The main component of a connection which holds the connected assembly together is bolt, with regard to the reaction which the connection has to sustain the bolt, no of bolts and their pattern is designed.

The connectors are also called as fasteners because besides connecting the member they also play a prime role in transmitting force from one component to other. That is why they have to be design taking considerations of the loads which will act, as well as the reactions that would be generate in the structure. An inadequate or faulty connection can lead to failure of the structure. Primarily bolts are the first choice for connection than rivets and weld. Bolts are designed for their shearing and bearing strength minimum of which will give their design strength. Bolts are selected according to their sizes and strength, material made of, from respective codes.

 

Types of connections

  • a) Framed connections
         In this double angles are connected with bolts on either side of the web of the beam.
  • b) Shear End-Plate Connections
         The primary use of the shear end-plate is to resist gravity load. In this type of connection a shear plate is welded to supporting member and bolted to        connecting member.
  • c) Seated connections
          Where the beam reactions are very large that only shear connection is not enough in such situations we go with seat connection. In this a seat angle         is added to provide an extra support to the connecting member. There are mainly two types of seated connections,
    1) Unstiffened seated connection
         In this arrangement a seat angle bolted to the column supports the end of the beam. This seat angle also helps during the erection of the beam to its       position.
    2) Stiffened seated connection
  • Stiffened as the name suggest its self is to provide stiffness to the connection which is acquired by providing stiffeners to the connecting members which will give stability to the member.
  • d) Moment resistance bolted connection.
  • There are instances when connections are required to transmit moments in addition to shear loads in such situations a double angle connection with a cleat angle and seat angle is provided.

Steel Hangers

Steel Hangers

Hanger steel structure is kind of durable and strong material. With light weight, easy installation, simple transport, high safety. It is widely used in many fields, such as factory, civil engineering, warehouse, stadium. For pressure loads it include heavy steel structures and lightweight steel structures. Heavy steel Structures is mostly applied for industrial use, light steel structure is mainly applied for temporary house. Steel Hangers are having high durability to carry the load with particular weight applied on the beams at the time of construction. Steel Hangers consists of Truss and Frame elements which helps to distribute the load on all the support elements. 

Steel Hangers are connect with the Angle Sections on both the ends and further both the ends are connect with the gusset plate to main element.Steel Hangers are especially use in the factories and warehouse as it is easy to construct with Low construction Cost and disassembling of the hanger structure is easy.  As the Steel hangers are connect at the topmost portion of the roof which gives the comfort space on the floor for the storage purpose and commercial use. 

 Steel Truss Hangers are widely used in the steel construction industries, Because truss element can be construct at regular intervals for roofing and load carrying purpose.  Hangers are essential for protection from weather, direct sunlight and for maintenance, repair, manufacture, assembly, of aircraft. An alternative to the fixed hanger is a portable shelter that can be used for aircraft storage and maintenance. Portable fabric structures can be built up to 215 ft (66 m) wide 100 ft (30 m) high and any length. They are able to accommodate several aircraft and can be increased in size.

Structures And Sizes

Hangers need special structures to be built. The width of the doors have to be large, this includes the aircraft entrance. The bigger the aircraft to be introduced, the more complex a structure is needed. According to the span of the hangers, sizes can be classified as:

                                         SIZE                                                                                                                                                SPAN
                                        Small                                                                                                                                         Less than 30m
                                       Medium                                                                                                                                             30-60m
                                         Large                                                                                                                                                 60-90m
                                      Extended                                                                                                                                             90-120m
                                   Continuous                                                                                                                                     More than 120m
Continuous hangers are built for the largest aircraft and building codes in the countries and jurisdictions and airports where they reside.

Welded Connections

Welding Connections

Another type of connection which is hardly visible to people is welded connection. When we say this it
doesn’t mean that it is invisible but its visibility is quite like the material in contact and the finishing work
that has been done on it. When we apply any adhesive material we tend not to make it visible from
outline areas so that it looks pleasing same is with the welded connections. One must be think why
welding, when we can have bolted connection? Why welding is needed when it is this much difficult?
The answer is that, Every time it is not possible to provide bolted and riveted connection due to reasons
like:

  •  Less area is available for bolts or rivets
  •  Material thickness is not that enough to add bolts.
  •  Rivet and bolted connection are heavy weighted and increases total weight of structure when it
    is undesirable.
  •  Welding eliminates the need for splice plates instead of bolted connections which every time
    requires a splice plate for its connection.
  •  A bolted connection provides some percentage of flexibility to the connection whereas welded
    connection provides rigidity.

What is welding?

Welding is a process of connecting metal parts by fusion. When you see a chair, table made of metal their joints are connected through welding only, in a similar way in steel structures the supporting member or the connecting member is welded to the components of connection. Welding is a critical process but very crucial also. It requires perfection because any fault in welding can be dangerous and can sometimes be unpredictable, so in order to provide welding the person must be experienced one. Welding also depends on the parts that to be welded along with the filler material. Most of the welding works are carried out during fabrication process and some of the methods that are used for welding are,

  •  Shaded metal arc welding (SMAW)
  •  Submerged arc welding (SAW)
  •  Gas metal arc welding (GMAW)
  •  Flux cored arc welding (FCAW)
  •  Electrogas welding (GMAW- EG) or (FCAW-EG)
  •  Electrogas welding (ESW)
  •  Stud welding
  •  Resistance welding

Selection of type of weld

Above given welding processes are select by the steel contractor according to the design requirements and productivity point of view. The weld length, round of weld and size of weld that should be provide are detail in the sheets but the fabricator must be aware of the actual possibilities that can get arise while erection.
Types of Weld that are used in steel structures are:

  •  Fillet weld
  •  Groove weld
  •  Plug welds and slot welds

Generally most of the welded connections are fillet because they are easy to prepare, easy to apply and can be easily done in an inaccessible areas. One must know these fact that a complete connection is not generally achieve by only welding or only bolting, sometimes or we can say now a days most of the structures have combine connection type, it might be shop weld. Or field weld. Some common welded connections are

  •  Shear connections
  •  Seated beam connections
  •  Eccentric welded connection

Industrial steel structure

Industrial Steel Structure

Factory structure

Why steel structures are common to every industry? The simplest answer is space. Space accommodation is best available through steel structures only. It is very important to have an effective space management in industries like manufacturing (automobiles, food production), processing rubber,textiles, pharmaceutical.

When an industry grows, its demands as well as its capacity also increases. And at such times we require more space to handle the growing output. Suppose you have only concrete structures and you want to expand for more storage. Is it possible to build without destructing the structure? It’s no. Because a concrete structure is immovable and need to be demolish first for next construction All these things require a huge amount of time with variable cost. Industries are time bounded because the products need to be furnish on time to be available in the market on time.

Hence these problems are overcome by steel structure. If the industries expand and need more space for more equipment or installations then just remove the bolted assembly and place them on the desired location. Or you can introduce a new supporting assembly also. Every movement of structure does not create any disturbance in the working of industries therefore it is very suitable.

Advantages of using steel structure

 The layout and components can be design so that parallel rather than sequential construction can take place

 Interfaces between trades need to be minimize

 Collaborative discussion between trades will be need to ensure that, whatever is decide, all aspects 

 Construction can proceed quickly and safely.