Framed structures

Framed structures

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  FRAMED STRUCTURES SUBMITTED BY:- SUBMITTED TO :- Vidushi Gupta (13/AR/012 ) Nirmita Mehrotra Ma’am Shivangi Saini ( 13/AR/010 )
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  Framed buildings arebuilding structures formed by the framed elements usually in the form of columns and beams, as well as further strengthened as necessary by the introduction of rigid floor membranes and external walls. Common forms of framed building structure subdivided into 2 main types: DEFINITION INSITU RC FRAME PREFABRICATED FRAME STEEL STRUCTURE
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  RECTANGULAR FRAMED STRUCTURES •Aframed structure is a network of beams and columns joined up to form the skeleton framework of the building. •The structural frame carries the total load of the building and transfers it to the foundation. •Cladding is fixed over the framework, or infill panels are placed between its members, to totally enclose the space within the building. •Framed structures are easily erected from pre-made members. •These members are easily connected together in the correct sequence to form the structural framework.
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  • Problems arisewhen large members are used and when the height of the structure makes lifting difficult. • In these situations a crane will be needed to lift the members into place. • Rectangular frames are usually made from steel but they may also be made from concrete. • The multi-storey car park under construction is a concrete framed structure. • They are set a right angles to each other to provide support for the floors, walls and roof
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  A STEEL FRAMEDSTRUCTURE IN COURSE OF ERECTION Rectangular framed structures are used for multi-storey buildings such as: Office Blocks Large Schools Hotels Hospitals or other similar buildings where a multi-storey structure is required. The floor space will incorporate a large number of columns.
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  ADVANTAGES • Speedy constructiondue to simplicity in geometry – consist of only columns and beams as the main structural elements • Rigid and stable – able to resist tremendous vertical (dead load) and lateral loads (wind) • reduced dead load – absent of thick shear wall etc. • Roofed over at an earlier stage – every floor slab being finished becomes an cover to protect the lower floors from sun and rain • offer large unobstructed floor areas – without obstacle between columns • flexible utilization of space. • Adaptable to almost any shape • easily altered within limits of frame – regular or non-regular grid system is very adaptable in spatial arrangement • offsite preparation possible – especially for prefabricated construction using precast concrete or structural steel elements
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  PRINCIPLES OF DESIGNINGFRAME STRUCTURES As already indicated, the primary function of a skeleton frame is to carry safely all the loads imposed on the building and this is must do without deforming excessively under load as a whole or in its parts. In order to fulfill this function efficiently it must provide in its design and construction adequate: • STRENGTH AND STABILITY These are ensured by the use of appropriate materials in suitable forms applied with due regard to the manner in which a structure and its parts behave under load. • FIRE RESISTANCE An adequate degree of fire resistance in the frame is essential in order that its structural integrity may be maintained in the event of fire, either for the full period of a total burn-out or for a long period at least long enough to permit any occupants of the building to escape.
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  COLUMN Columns and strutscarry load primarily in compression along their length, and are found in most building structures. So, principles or criteria of column design can explain as: • The strength of stocky columns is related to material strength. • The strength of slender columns is limited by buckling. • In practice steel columns have to allow for both buckling and material failure, and for interaction between the two. • The resistance of a cross-section to buckling is represented by its radius of gyration. • End conditions influence buckling behaviour and are accounted for by using an effective length. • In practice columns are subject to a combination of compression and bending. • Because buckling resistance and actual stress are both related to the size of the cross-section, iterative design procedures must be used.
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  BEAM he composite beamdesign is concerned with sizing the steel section. The philosophy of designing composite beams is to utilize the implicit strength of the concrete slab. The form and thickness of this will have been determined by its functional requirements as a slab. Design may be governed by any of the following criteria: • Deflection - the stiffness of the beam will be chosen to minimize deformation. • Vibration - the stiffness and mass are chosen to prevent unacceptable vibrations, particularly in settings sensitive to vibrations. • Bending failure by yielding - where the stress in the cross section exceeds the yield stress • Bending failure by lateral torsion buckling - where a flange in compression tends to buckle sideways or the entire cross-section buckles torsionally • Shear failure - where the web fails. Slender webs will fail by buckling, rippling in a phenomenon termed tension field action, but shear failure is also resisted by the stiffness of the flanges
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  CONTENTS Shear Walls Moment ResistingFrames Braced Structures EARTHQUAKE RESISTIVE FEATURES IN FRAME STRUCTURES
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  1. SHEAR WALLS •First used in 1940, may be described as vertical, cantilevered beams, which resist lateral wind and seismic loads acting on a building transmitted to them by the floor diaphragms. EFFECTS IN EARTHQUAKE Building frame system with Shear Walls Typical arrangement of shear walls
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  • A simplebuilding with shear walls at its ends. Ground motion enters the building and creates inertial forces which move the floor diaphragms. This movement is resisted by the shear walls, and the forces are transmitted back down to the foundation. Shear wall: vertical analogy as cantilever beams 2. MOMENT-RESISTING FRAMES Moment-resisting frames are structures having the traditional beam-column framing. They carry the gravity loads that are imposed on the floor system. The floors also function as horizontal diaphragm elements that transfer lateral forces to the girders and columns. In addition, the girders resist high moments and shears at the ends of their lengths, which are, in turn, transferred to the column system. As a result, columns and beams can become quite large.
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  MOMENT-RESISTING FRAMES ■ Moment-resistingframes can be constructed ofsteel, concrete, or masonry. ■ Consist of beams and columns in which bending of these members provides the resistance to lateral forces. ■ There are two primary types of moment frames, ordinary and special. ■ Special moment-resisting frames are detailed to ensure ductile behavior of the beam-to-column joints and are normally used in zones of higher seismicity. ■ Steel moment-resisting frames have been under intensive study and testing.
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  3. BRACED STRUCTURES •Braced frames develop their resistance to lateral forces by the bracing action of diagonal members. The braces induce forces in the associated beams and columns so that all work together like a truss with all members subjected to stresses that are primarily axial. • Braced frames act in the same manner as shear walls, though they may be of lower resistance depending on their detailed design. • Bracing generally takes the form of steel rolled sections, circular bar sections, or tubes; vibrating forces may cause it to elongate or compress, in this case it loses its effectiveness and permits large deformations or collapse of the vertical structure.
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  • Bracing canbe used to stop buildings swaying over. It helps buildings stand up to the sideways forces that can occur during earthquakes or high winds. Bracing members can work in tension or in compression. EFFECTS OF EARTHQUAKE 4. BRACED STRUCTURES