What do you know about (Portal Frame Method) in structures and bridges?

Thank you Mr. Quliai.

Portal frame construction is a method of building and designing structures, primarily using steel or steel-reinforced precast concrete although they can also be constructed using laminated timber such as glulam. The connections between the columns and the rafters are designed to be moment-resistant, i.e. they can carry bending forces. "They were first developed in the1960s, and have now become the most common form of enclosure for spans of20 to60 m"

Because of these very strong and rigid joints, some of the bending moment in the rafters is transferred to the columns. This means that the size of the rafters can be reduced or the span can be increased for the same size rafters. This makes portal frames a very efficient construction technique to use for wide span buildings.

Portal frame construction is therefore typically seen in warehouses, barns and other places where large, open spaces are required at low cost and a pitched roof is acceptable.

Generally portal frames are used for single-story buildings but they can be used for low-rise buildings with several floors where they can be economic if the floors do not span right across the building (in these circumstances a skeleton frame, with internal columns, would be a more economic choice). A typical configuration might be where there is office space built against one wall of a warehouse.

Thank you my dear 

Portal frames are generally low-rise structures, comprising columns and horizontal or pitched rafters, connected by moment-resisting connections. Resistance to lateral and vertical actions is provided by the rigidity of the connections and the bending stiffness of the members, which is increased by a suitable haunch or deepening of the rafter sections. This form of continuous frame structure is stable in its plane and provides a clear span that is unobstructed by bracing. Portal frames are very common, in fact50% of constructional steel used in the UK is in portal frame construction. They are very efficient for enclosing large volumes, therefore they are often used for industrial, storage, retail and commercial applications as well as for agricultural purposes. This article describes the anatomy and various types of portal frame and key design considerations.

 Thank you my dear brother about invitation ,,, Portal frames, used in several Civil Engineering structures like buildings, factories, bridges have the primary purpose of transferring horizontal loads applied at their tops to their foundations.Structural requirements usually necessitate the use of statically indeterminate layout for portal frames, and approximate solutions are often used in their analyses. Assumptions for the Approximate Solution .In order to analyze a structure using the equations of statics only, the number of independent force components must be equal to the number of independent equations of statics. If there are n more independent force components in the structure than there are independent equations of statics, the structure is statically indeterminate to the nth degree. Therefore to obtain an approximate solution of the structure based on statics only, it will be necessary to make n additional independent assumptions. A solution based on statics will not be possible by making fewer than n assumptions, while more than n assumptions will not in general be consistent. Thus, the first step in the approximate analysis of structures is to find its degree of statical indeterminacy (dosi) and then to make appropriate number of assumptions.

For example, the dosi of portal frames1,3,2 and1 respectively. Based on the type of frame, the following assumptions can be made for portal structures with a vertical axis of symmetry that are loaded horizontally at the top

1The horizontal support reactions are equal

 2There is a point of inflection at the center of the unsupported height of each fixed based column

Assumption1 is used if dosi is an odd number (i.e., =1 or3) and Assumption2 is used if dosi1.

Some additional assumptions can be made in order to solve the structure approximately for different loading and support conditions.

3Horizontal body forces not applied at the top of a column can be divided into two forces (i.e., applied at the top and bottom of the column) based on simple supports

 4For hinged and fixed supports, the horizontal reactions for fixed supports can be assumed to be four times 

Thanks for invitation,

Portal frame method(Rigid frame system) seems to be economical up to approx.30 storeys for steel framing and up to20 storeys for concrete framing. Because of its continuity the rigid frame responce to lateral loads primarily through flexure of the beams and columns, this continuous character of the rigid frame is dependent  on the rotational resistance of the member  connections not permitting any slippage.

The load capacity of the frame relies very much on the strength of the individual beams and columns , its capacity decreases as storey height and column spacing becomes larger.

Rigid frame systems subdivided into :

1.Rigid frame-Shear wall Interaction

2.Rigid frame Shear Mode Defomation

3.Shear Wall Bending Mode Deformation

4.Interaction of Frame and Shear Core.

I agree with the esteemed professors and thank you for the invitation

Agree with the answers added by gentlemen’s.

Portal frame construction is a method of building and designing structures, primarily using steel or steel-reinforced precast concrete although they can also be constructed using laminated timber. The connections between the columns and the rafters are designed to be moment-resistant, i.e. they can carry bending forces.

Portal frames are frequently used over the entrance of a bridge and as a main stiffness element in building design in order to transfer horizontal forces applied at the top of the frame to the foundation. On bridges, these frames resist the forces caused by wind, earthquake, and unbalanced traffic loading on the bridge deck. Portals can be pin supported, fixed supported, or supported by partial fixity. The approximate analysis of each case will now be discussed for a simple three-member portal.

As with all software, you need to know what you fill in and interpretate what comes out and need to understand that. So you need to know the basics without any software. Then the software can save you time!

At my office the second week my stagaires came to work, I took away the Computer on Friday and asked them to take there books on Monday and basic skills to solve a structure.....Panic!

another example: One time a student used our programs and said: the structure fails... I asked , at what point: answer: the computer says so.....

Need I say more?

Portal Method is used to analyze a laterally loaded frame (seismic and wind load).