5. Mechanical properties of materials

This chapter offers infomation on the different structural materials. The materials are compared on a few characteristic aspects. More detailed information can be found in the chapters.

5.1. Construction types and spans

Fig. 5.1 Construction types and spans.

5.2. Material properties

Property	Timber	Steel	Concrete (in situ)	Concrete (prestressed and/or precast)
Self Weight	Small (4 to 10 kN/m³, depending on the species)	Large (78.5 kN/m³) but relatively low self weight, large spans are possible (optimized cross sections); steel use per m² roof area: 0.3 to 1 kN	Large (24 kN/m³), this has consequences for the foundation and maximum span; not economical with low variable load	Large (24 kN/m³), this has consequences for the foundation dimensions; fairly large, but favorable with respect to buckling and deformation limits
Fire Resistance	Small dimensions have low fire resistance; Larger sections have good fire resistance	The structure has low fire resistance, but does not burn itself	Good resistance if the cover is sufficient	Less resistance than in situ concrete due to deterioration of the prestressing steel. Does not collapse easily, but is not reliable after a fire
Water Tightness	Dependent on the application	Not applicable	Good	Good
Thermal Properties	Not susceptible to thermal influences	Sensitive to temperature changes; bad without insulation	Low thermal insulation, beware of thermal bridges	Low thermal insulation, beware of thermal bridges
Acoustic Properties	Acceptable to good; sound reflection is high with corrugated sheet metal in roofs and walls	Air sound insulation is good, contact sound insulation is bad	Air sound insulation is good, contact sound insulation is bad	Adaptability in relation to doors, windows, etc. is good, if the appropriate measures are taken in advance
Adaptability	Good	Good	Good, if the appropriate measures are taken in advance	Standard product; tolerances must be incorporated in the design
Adaptability to ducts	Trusses are especially suitable for carrying trough of ducts; connection can be done fairly easy	Information is needed upfront and must be processed very accurately. After casting, extra measures are difficult to incorporate	Limited possibilities upfront. After casting, adaption is very difficult	Low
Suitability for later adjustments	Good	Good	Difficult	Low
Labour intensity	See steel. A lot of preparation in the factory, resulting in fast and simple assembly on site	The formwork and falsework are very labour intensive. If possible, use standard formwork. Avoid small amounts of concrete at great heights	Factory product with fast assembly on site. Extra stressing on site requires specialized tools and crew	N/A
Necessity of serial production	Not necessary	Not necessary	Preferred, but less necessary than with prefab concrete	Necessary, because of the high costs of moulds
Residual value after demolition	Low positive residual value, but demolition is easy	Positive residual value; demolition is expensive	Negative residual value	N/A
Erection speed	Fairy quick	Short construction time	Low construction speed due to the time needed for hardening, reuse of formwork, and influences of the weather	Fast montage, but delivery and hardening times must be accounted for
Needed construction site	Limited	Small	A lot of space needed for preparation of formwork and reinforcement	Small
Hygiene	When the correct sections are used, almost no dust collection on certain profiles	Dust is easily collected	Very suitable for dust-sensitive structures	Good, partially dependent on cross-section