Knowledge map -week 4 Span & spacing floor s p an
floor
s p a c i ng
Floor
Span is the distance measure between two supporting element, it can be measured vertical or horizontal. It measures from the bottom of the up floor to the next floor above. Spacing is the repeating distance measured between a series of like or similar element such as beams and columns, it can be measured vertical or horizontal. It measures from the CENTER of the bottom of the up floor to the CENTER of the next floor. span should not exceed 24x joist depth * SPANCING always depends on the SPANNING capacities(magnitude) of the supporting elements. Such as floor load, the load-caring capacity of the joists and the floor construction depth desired.
three main floor system: joists further apart: larger span, then the support need to be strong. Concrete system: slabs of various types are used to span betweens structural supports, these can be one0way or two way spans. How to choose the distance between the two supporting element, further apart? Or close together? The efficient of the function of the buildings. If its an office buildings, then what type of the system should we use? Main component Stone: concrete-artificial stone • Cement is mixed with water it binds the sand and gravel aggregates together to make the hard, solid material. Commonly, 1 part cement(portland or lime): 2 parts fine aggregate(sand): 4 parts coarse aggregate(crushed rock): 0.4-0.5 part water. The reaction called 'Hydration'. • The moulds used to hold the liquid concrete in place until it becomes hard-- 'Formwork'. It can be building IN SITU or in PRECAST. Timber metal etc could be used, when the concrete is hardened, the formwork is often removed, stored and reused or it may stay in place forever. (sacrificial formwork) 1. too much water: weak, not strong enough 2. too little water: too stiff, unworkable Advantages: it is fluid and shapeless before it hardens. The shape can be formed into any shape Curing Process - use props and bracings to support the concrete during process because it self is very heavy. -reaches 75% approximately 7 days with testing, complete around 28 days Reinforcement
• very strong in compression, but weak in tension. • Add mesh or bars to get it more tension- reinforced concrete. • Reinforcement quantity may add more on the base of the buildings. Properties: • high hardness, can be scratched with a metallic object • low fragility can be chipped with a hammer • very low ductility (延伸性) • low flexibility or plasticity • medium porosity, more waterproof • very durable • not easy recycle • high embodied energy • cost effective – formwork and purring into Consideration • permeable (有渗透性的), not completely waterproof, • if the steel bars are too close to the surface, the moisture may go through and oxidation (氧)causes aesthetic(outside look) and structural degradation of the concrete. • Poor vibration of the concrete during pouring process. Such as vibrated to get rid of the air bubbles. If the bubbles can not be removed, it can compromise the structural performance of the element, even wrose result in the element failing. Steel system: -open web joists: efficient& expensive. Water pipe can be carried from open web joists. Girders (main beams) -sometimes combine with concrete slab systems to where the particular benefits of steel framing and shallow depth floor slabs systems are desired. To choose steel or concrete? Cost and the size and the function of the building, such as hospital always use concrete sytem reinforcement • very strong in tension timber systems: traditional • joists(secondary beams) to support the floor board, support on bearers(primary) • floor board 450-600mm spanning so put close together. • floor system always uses joists. Advantages • renewable material, • quicker than concrete. • Less cost, higher return because the faster complete on construction process, the quicker on returning money. Floor system to transfer dead and live loads via horizontal members to supports. •
Horizontal or diagonal bridging is required to prevent lateral movement of joist chords
horizontal bridging angles are welded to top and bottom chords diagonal bridging angles used for LH/DLH series joists. Advantage why precast concrete may be preferred over in situ concrete. • Precast concrete's quantity may be more preferable, but hard for transport. • in situ concrete easily shaded