The steel structure refers to the part of civil engineering, in which for the construction of structures primarily steel is used.
In steel construction, rolled steel beams, plates and tubes made of structural steel by screwing, welding or rivets are interconnected to form a structure. Another key design element of the steel structure is the gusset plate, which connects the individual bars of the structure together. Besides the pure steel construction, there is also the steel composite construction that combines steel elements with concrete and the steel - skeleton construction. The Design of steel structures is usually done by Euro code 3: Design of steel structures ( EN 1993 )
The steel structure combines the advantage of the relatively short planning and construction, with a flexible design of the structure. This flexibility results, for example by the use of relatively lighter and slimmer, heavy-duty components and a high, as well as precise degree of prefabrication, reducing installation times. Steel components that are exposed to the weather must be protected against corrosion by surface coatings or galvanizing. The fire protection can be ensured if necessary by the fire protective covering or fire protection coatings. In recent years, increases the importance of building long-term plan to build and operate, more and more. The players in the construction and real estate industry to develop a holistic view of their projects. Hardly any other building material is so well suited for sustainable construction such as steel: Due to its high strength, it can easily carry all the skyscrapers even with low structural weight and delicate structures. If these later once built, the steel used can be separated with magnets from the mining waste. Already, 11% of the collected steels are directly reused in new buildings, the rest can be converted into high-grade steel as secondary raw materials (scrap) again. The new steel can even get a higher strength than the starting material. The slight increase in cost for structural steel often relativized by a rapid deployment phase, flexibility of the support structure through wide spans, and the reusability and recyclability of steel structures against ostensibly cheaper constructions as bz.B. those of reinforced concrete. They appear basically used everywhere useful where high strength requirements are placed on the design, for example, in large-span roof structures in steel - skeleton or example, if aesthetic, formal design reasons require slender structures.
The steel structure is divided into
- Steel lattice towers
- Bridge including composite bridges
- Hydraulic Steel
In general, steel structures must be protected against corrosion. This is usually done by coating the structure with anti-corrosion paint or hot dip galvanizing. The corrosion protection is governed by the standards of the EN ISO 12944 or EN ISO 1461. Since steel has a high affinity for oxygen results in the oxidation, thus a transition from a high energy state to a low energy metal oxide state. With other metals such as aluminum and zinc, the metal is protected from further oxidation by the formation of a highly dense oxide layer. The atmospheric corrosion of steel forms in the presence of oxygen and water ( with a humidity of about 65%) rust, chemically FeOOH, which is further accelerated in aggressive atmospheres (salts, especially chlorides or acids). Rust (FeOOH ) having 25.37 cm ³ / mol 3.6 times the molar volume of iron ( 7.1 cm ³ / mole). Therefore, the volume of iron increases due to corrosion by at least this factor, see Pilling - Bedworth ratio. By porosity and water retention, the increase in volume can also be much larger. This increase in volume causes spalling of coating materials around defects in a coating.
When corrosion protection there are two different systems: a) coating and b) metallic coatings. Coatings consist of a shop primer, a base coat (previously mostly zinc chromate or red lead, nowadays usually pigmented (zinc dust, zinc phosphate) resin coatings) and a top coat ( at least 2 -layer order, as protection against moisture and UV rays ), the coating materials of pigments, binders and fillers are made. Metallic coatings consist of a metallic protective layer for mild steel mostly in the form of a hot-dip galvanizing in immersion baths. Due process molten zinc bath must be feuerverzinkungsgerecht designed to be galvanized steel parts prior to immersion in the 450 ° C. Another corrosion protection to steel members are called duplex systems that combine a hot-dip galvanizing with a subsequent coating. Duplex systems are used when steel is to be extremely long protected against corrosion.
With ropes of interior protection is provided by cavity filling during the stranding with linseed oil - red lead paste, while the outer protection is provided by a high build, elastomeric plastics, which do not hinder the relative movements and deflections of the individual members.
In addition, the steel components should already be protected by the shape and arrangement to the possibility of corrosion: prevention of water pockets and dirt, free accessibility of the metal parts, or air and water vapor tight closure.
Steel structures often require special fire protection, since the thin-walled cross-sections of supporters and their good thermal conductivity quickly heat these in a fire and thereby reduces their strength. Depending on the fire load and the intended use of the building can be matched with one of the required fire resistance oversizing of the components or with special sheathing the failure of the structure can be prevented. The mechanical properties of the steel are temperature dependent, so that for example, the yield strength at 600 ° C to half of the value at 20 ° C is lowered. Also, the modulus of elasticity decreases with increasing temperature steel. One required by law for the particular building " fire resistance " must be maintained for fire protection, which is defined for common building each in the national building regulations of the federal states. This required fire resistance time is divided depending on the structure and use into categories, according to German standard (DIN 4102 - Fire behavior of building materials and elements ) in F30, F60, F90, F120 or F180. The numbers give the minimum value that the structure must withstand the fire in minutes. The assumable for the oversizing of the device or for the determination of the insulating fire protection measures " standard fire " is the standard temperature - time curve, also called short " ETK ". Describes a temperature -time curve according to which the gas is heated in temperature of a component testing. The the "protected " component surrounding gas temperature rises according to the specification of the EPC within the first few minutes steeply to about 600 ° C and then decreases slowly but steadily until failure of the component to. The time to failure of the construction is completed on the fire resistance classification of the standard. In this way provide any additional measures to protect a steel component, their performance profile to the test.
The methodology of the Überbemessens ( according to European Standard EN 1993-1-2 ), however, is based on a mathematical determination. The starting point is the numerical determination of the steel temperature in the ETK - fire with the required ( fire resistance ) duration. With the determination of the steel temperature can be determined necessary for the design of mechanical properties. The actual design is similar to the " cold" Rated with the heat-affected mechanical properties under the brand customized security values instead. On the basis of experiments of this design method was calibrated.
On steel component, retrofitted fire protection measures have insulating, shielding or heat-dissipating effect.
Insulating fire protection measures: the profile shape following sheathing and cladding of steel profiles in cementitious spray plaster with vermiculite or mineral fibers, usually with necessary plaster base. Composite columns systems ( construction of the Composite ) meet the requirements in most cases without additional measures. In addition, box- shaped housing (gypsum board, thickness and attachment is certified to the manufacturer ) [ F90 ⇒ possible] the steel profiles additionally a necessary corrosion protection order. Intumescent coating in the form of coatings ( spray / coating / paint roller ) are ( 2-4 coats about 300-1400 microns Equivalent ) to F60 realized with economically interesting layer thicknesses. With layer thicknesses of up to more than 3 mm (> 5 operations ) can be now intumescent coating for fire resistance class F90 (see approval Z- 19.11- 1794 of the DIBt - Web Links ) muster. The definition of the necessary layer thickness depends on the ratio of the cross-sectional circumference flamed from the cross-sectional area (U / A value), the profile type ( open or closed ) and the component type. Since Dämmschichtbildnerbeschichtungen form an orange skin-like surface due to the large layer thicknesses must when high surface quality is required, in addition an elaborate post-processing (grinding, smoothing ) to be made. Through the use of modern water-based systems, the orange peel can be largely avoided. (see approval Z -19.11 -1461 )
Shielding Fire protection measures: mostly already existing, space-enclosing systems such as suspended ceilings.
Heat dissipating fire protection measures: filling the steel profile cavities ( columns) with independent pumps, thermal freely circulating water. Especially useful in high-rise construction.
Any fire safety measure has your pros and cons. Therefore, aesthetic, economic, technical and security relevant factors should be carefully considered in planning.
Known structures of steel
- Eiffel Tower in Paris
- Berlin radio tower and dome of the Reichstag in Berlin
- Müngstener bridge
- Hohenzollern Bridge in Cologne
- Rendsburg High Bridge
- Viaduc de Millau in France with a bridge girders made of steel
- Garabit Viaduct in France
- Geulvalley Viaduct in Belgium
- Forth Bridge in Scotland
- Firth of Tay Bridge in Scotland
- Golden Gate Bridge in the United States
- Platform hall Frankfurt Main Station
- Killesbergturm in Stuttgart
- Eden Project in England
- Berlin Hauptbahnhof - Lehrter Station
- Parking garage on the motorway A8 of the New Stuttgart Trade Fair Centre
- Sydney Harbour Bridge
- Neumayer Station III