Beam design:
The design selected for the beam element encompasses the use of precast prestressed concrete. Two symmetrical beams supporting a cast in-situ slab was used so as to provide longitudinal torsional restraint. All in-situ concrete and formwork shall be carried out in accordance to SANS 10100 specifications as described by the calculations attached herein.
Precast design was selected since the beam can be produced under factory conditions and not necessarily cast on-site. Quality can be controlled and costs reduced since there is no need for complex scaffolding, and hence erection time and labour is lowered.
Construction method: Pre-tensioning
The wires are tensioned prior to concreting by means of jacking systems fitted to the beam mould. The concrete is then poured. When hardened, the prestressed beam is removed from the mould. It tends to bend upwards due to prestressing, but deflects to an approximately horizontal position when loaded. The contractor shall satisfy that during casting of concrete, the beds do not deform and contribute to loss of prestress. Only stressing steel that is clean and rust free will be accepted for tendon purposes. If deemed necessary by the engineer, all wires and strands must be treated with an approved anticorrosive before assembly.
Design specifications:
• Two 1200 x 400mm beams supporting a composite insitu slab.
• Beam concrete properties of 50 MPa characteristic strength with an elastic modulus of 35GPa. Unit weight of 24kN/m3 is used. A minimum cover of 30mm must be provided to all reinforcing.
• Class 1 beam, i.e. no tensioned induced throughout the beam in transfer and service conditions. Permissible stresses in accordance to design code specifications. The compressive strengths obtained according to the grade of concrete used is 20MPa in transfer and 16.5 MPa in service conditions.
• Analysis of loading conditions yields a permanent action of 20.55 kN/m and variable actions of 5kN/m2. Serviceability limit state is used to check bending in the beam while ultimate limit state is used for shear.
• The magnel diagram (see calcualtions) was plotted inorder to obtain the feasible region in determining the prestress force at a particular eccentricity. To increase accuracy, the diagram encompasses the service, transfer and construction conditions. A maximum eccentricity of 375mm at midspan with a prestress force of 3705kN was obtained. 18mm diameter 19 wire strands tensioned to 75% of the characteristic strength (370kN), while taking into account elastic losses of 5%, produced a requirement of 15 strands to carry the specified loading conditions.
A connecting rod subjected to an axial load F may buckle with x-axis as neutral axis in the plane of motion of the connecting rod, {or} y-axis is a neutral axis. The connecting rod is considered like both ends hinged for buckling about x axis and both ends fixed for buckling about y-axis. A connecting rod should be equally strong in buckling about either axis [8].
Ali, Mir M. Moon, Kyung Sun. “Structural Developments in Tall Buildings: Current Trends and Prospects” Architectural Science Review, Volume 50, Issue 3, 2007. Web. 27 Sept. 2017.
In the past two decades, light gauge (cold-formed) steel has rapidly become a frequently-specified construction material for commercial, institutional, and industrial projects - including the recent trend toward using steel as the main load bearing system. Despite the myths that still surround the use of light gauge steel framing, it has come to the forefront as the best and most feasible alternative building material for residential construction.
3) Super workable concretes have the ability to fill the heavily reinforced sections without internal or external vibration, without segregation and without developing large sized voids
[17] BS 4550-3.4:1978. Methods of testing cement, Physical tests, Strength tests. British Standards Institution ; 2007.
Concert can used for general building work such as , namely columns, beams and slabs
Concrete behaves as a back bone to nations building team. Concrete is a composite construction material composed primarily of aggregate, cement, and water. There are many formulations, which provide varied properties. But one of the disadvantages with the conventional concrete is high self weight of concrete. This heavy weight will make it some extent uneconomical structural material. Many attempts made in the past to reduce the self weight to increase the efficiency of concrete.
In our design, we feel that the geometric shapes and the dimensions we chose will greatly affect the outcome of our bridge. We expect this bridge to hold a great amount of weight because our cylinders will be reinforced and backed up by one another. Since our bridge has stacks and multiple levels, we expect it to be strong. When we stack the weights onto our bridge, the offset cylinders will act like triangles, evenly distributing weight in a fine pattern.
Bachmann, H., & Steinle, A. (2011). Precast concrete structures / Hubert Bachmann, Alfred Steinle. Berlin: Ernst & Sohn, c2011.
A beam is a simple design of a support structure. The major characteristics of this type of structure is its ability to span over
The continuous strain, which the concrete undergoes due to application of external loads is called……………………………………….
Generally outriggers take the form of trusses when made of steel, and walls when made of concrete, as they are to transmit substantial loads along the building in order to mobilize a tension-compression couple in outer columns, outriggers are often position at several heights and tend to be at least two stories high, both to insure structural solidity and to minimize view obstruction from within the
Chua, Ian Y. H. Civil and Structural Engineering Resource Web. 29 Jan. 2000. 2 Mar.
It is possible to develop a customized solution using such formwork systems for any type of building for example a framed structure involving column beam slab elements or for a box-type structure involving a slab-walls combination.