Lecture 4 Beams - Building Construction - PDF

Mousl university2nd semester : Building Construction Architecture department2 Date : xx / xx / xxxx Iraq Elements of skeleton system 2.Beams Building Co...

Mousl university2nd semester : Building Construction Architecture department2 Date : xx / xx / xxxx Iraq Elements of skeleton system 2.Beams Building Construction 2 Assistant Teacher. : Adil Khalil Beam is a horizontal element of a structure and spans between one or more supports. Every beam has a purpose: In general ,if something is to be kept on an opening, we need a beam. However, there could be other situations need a beam 1.Tying columns together. 2. Supporting masonry above 3. Supporting slab above : This is most common function of a beam. 4. Supporting slab below : This you shall see in a porch or in a sunk portion of the toilet. 5. Supporting secondary beams : 6. Suspending accessories: 6.1 Electrical luminaries 6.2 Electrical cables 6.3 Air handling ducts 6.4 Suspended ceiling 7. Supporting water tank above  OBSERVE THE GRID OF BEAMS IN THE STAGING OF THIS HUGE OVERHEAD WATER TANK Normal load distribution: In a RCC framed structure, the load of occupants is taken by a slab which gets transferred to a beam. Beam transfers this load to column Geometry of a beam: Most common geometry of a beam is rectangular. The depth of beam shall always be larger than the width. This beam is stronger than if beam width is larger than the depth. TYPICAL RCC FRAMED STRUCTURE This rule shall be derived only in the case of a band WITH BEAMS & COLUMNS since width shall be 115 mm but depth is 75mm. BAND BEAM OR PATLI WITHIN THE AAC BLOCKS PARTITION WALL Criterion of beam design: Beam depth is derived as follows: 1.It should be the maximum stress on the beams shall not exceed the safe stress limits for that material. 2.The deflection shall not exceed the specified limits. Types of beams: Based on their function beams can be grouped as : 1.Below the plinth(In Substructure foundation) 1.1Tie beam 1.2 Ground beam 1.3 Plinth beams: Beam laid above the foundation I.E. at plinth level. Its the first beam framework constructed in the skeletal structure : PLINTH BEAMS IN A RESIDENTIAL BUILDING Tie beam  plinth beam Ground beam 2.Above the plinth( In Super-structure) 2.1 Sill beam: Below the window 2.2 Band beam 2.3 Lintel 2.4 Roof beams  Lintel Sill Band beam Roof beams 2.5 Supporting masonry above beam in the perimeter of a building spanning columns, and usually supporting floor or roof loads. 2.6 Hidden beam This name is given because this beam is not visible after slab is cast. Basically slab is not designed to take direct load of a masonry wall. The hidden beam receives wall load and transfers to main beams. 2.7 Inverted beam : When the slab is below the beam , such beam is known as the Inverted beam. This is usually provided at 3 situations : 1. Sunk slab for the toilet 2.Porch beams 3.Staircase mid landing  PORCH. with CANTILEVER INVERTED BEAMS and SIMPLY SUPPORTED SLAB 2.8 Coping beam. This provided at the top of a masonry parapet wall in order to protect the bricks from getting dislodged due to wear and also to provide a bracing to the wall. Quite often , reinforcement is avoided in coping and only concrete is cast in a rectangular shape. Note : Difference between a Plinth beam & a Coping is that: there is nothing on top of Coping where as masonry is continued after Band beam.  PLINTH BEAMS COPING AT THE TOP OF A BRICK MASONRY PARAPET. 3.Based on the supporting pattern, beams can be classified as below: 3.1 Simply supported : Two supports 3.2 Cantilever beams: Only one support 3.3 Continuous beams: More than two supports 3.4 Overhang beams : Two supports :.1 Simply supported beam: A simply supported beam is a type of beam that has pinned support at one end and roller support at the other end. Depending on the load applied, it undergoes shearing and bending. It is the one of the simplest structural elements in existence. The following image illustrates a simply supported beam. Simply Supported Beam(  we can see the simply support in practical life in bridge decks, precast beams. : 2. Cantilever beam : A cantilever beam is fixed at one end and free at other end. It can be seen in the image below. 3. Overhanging beam: A overhanging beam is a beam that has one or both end portions extending beyond its supports. It may have any number of supports. 4. Continuous beam: A continuous beam has more than two As the name suggests, fixed beam supports distributed throughout its length. It is a type of beam whose both ends can be understood well from the image below are fixed. Simply supported beam: A simply supported beam is the one which has hinged support at one end and a roller support at the other end. Hinged support is provided so that no moment could act on the support and, roller support is provided such that there should be no axial(horizontal) force on the member. Continuous beam: A continuous beam is the one which has hinged support at one end and more than one roller support in the entire span. The hinged support is used to bear horizontal and vertical forces with zero moment at end support. Other roller supports will experience vertical reaction only. Here bending moment act in the beam above intermediate support(except extreme end supports). Note: A continuous beam can have a variety of intermediate supports. Differences between simply supported & continuous beam A simply supported beam is used when we have to transfer the load to the support in the form of linear reaction only(not bending moment). In this case beam has zero bending moment at supports. A continuous beam is used when the span is large enough and construction of component in fragment is either not plausible or is not economical. In this case beam carries a non-zero moment at intermediate supports. 4.Based on their shape in plan , ( or how do they appear from above) the beams can be divided into: 4.1.Straight horizontal beams: 4.2 Straight inclined beams: 4.3 Curved beams: 5.Some beams are just unique and need special mention: 5.1 Pergola:‫عريشة‬ Set of beams at smaller spacing which don’t have a slab above. This is mainly an architectural feature and usually given at the terrace level. PERGOLA:LOOK AT THE TOP OF THE WHITE BUILDING. DO YOU SEE SEVERAL BEAMS WITHOUT A SLAB ? THAT’S PERGOLA. 5.2 Grid beams: Set of beams in two perpendicular directions and at a closer spacing which together support a slab above  5.3 Portal beam: GRID BEAMS WITH SLAB Portal is a structure which has integrated beam and two columns. 5.4 Arch: The interesting thing about arch is that it is ARCH BEAMS a compression member. It has a concept of pre-stressed concrete