《建筑材料》课程教学资源（文献资料）Advances in materials applied in civil engineering.pdf

Advances in materials applied in civil engineering K. Flaga Cracow University of Technology, ul. Warszawska 24, 31-155 Cracow, Poland Abstract This paper outlines the problems of the construction materials being used in civil engineering at the end of the 20th century and also of the construction materials of the future. The progress that have been made in the domain of basic construction materials such as steel and concrete over the 19th and 20th centuries is analysed. It is described how new materials such as carbon ®bre reinforced polymer, highstrength concrete and high-performance concrete, create the possibilities of a further development. New opportunities for modern gluedtimber structures are also presented. The limitations of the application of glass and plastics as construction materials are indicated. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Steel; Concrete; High-strength concrete; High-performance concrete; Carbon ®bres reinforced polymer; Bridges; Tall buildings; Offshore structures 1. Introduction Civil engineering Ð the art of construction of all kinds of buildings Ð has been at man's service since the beginning of civilisation evolution. These buildings are dwelling as well as public buildings, industrial buildings, bridges, viaducts, tunnels, roads and railways, highways and airports, liquid reservoirs and loose-material containers, weirs, dams, offshore structures, TV towers, and a lot of other structures that form the environment that we live in. Human activity in the ®eld of civil engineering goes far back into the past, when man observing nature around him began to imitate and to improve it in order to create safer and better living conditions. Moreover, relatively early he noticed that his engineering ``works'' apart from reliability, durability and functionality had to have elements of harmony and beauty. The same opinion was expressed by Socrates when he said that everything created by man should be functional, durable and beautiful. The development of civil engineering in the course of centuries meant a constant struggle with available materials, spans, or height, active loads and the forces of nature Ð water, ®re, wind and earthquakes. Some of those elements have primary and the other secondary signi®cance. Amongst those mentioned ®rst, an essential role has always been attributed to the in¯uence of the material on construction development. First of all, ancient communities had at their disposal natural materials such as stone and timber. In the course of time, they learned how to use clay to form bricks, an arti®cial stones, which were ®rst dried only in the sun and then baked. In the main civilisation centres (the Middle East, the Near East, and the Mediterranean region) the hot climate and inconsiderate economy led, in a short time, to the elimination of timber as a building material. It did not happen in the wood-abounding countries of Middle and Eastern Europe, Scandinavian and the Asiatic part of Russia. Stone and brick Ð brittle materials Ð dominated civil engineering in the region of European civilisation for several centuries: from stone pyramids in Egypt 3000 years B.C. until the so-called First Industrial Revolution in England (the turn of the 18th and 19th centuries). They were suitable building materials for erecting walls and columns but at the same time, due to their low tensile bending strength, they caused a lot of problems in horizontal elements. Therefore a vaulted arch that was popular in ancient Rome, semicircular in its primary form, was the pattern that was to be employed for elements or structures of larger span. The arch in the course of time became lighter and less massive. The ratio of span-to-width of piers carrying vertical and horizontal loads became increasingly greater. During the early Middle Ages no improvements were implemented. It was not until Gothic and the Renaissance that new forms and ideas were introduced. However, still they were always based on elements that were in the forms of arches, curvilinear vaults with more and more developed forms (e.g. cloister vault, cross vault, barrel vault, lierne vault). The arch changed from semicircular to segmental (e.g. Ponte Vecchio in Florence) and ®nally Journal of Materials Processing Technology 106 (2000) 173±183 0924-0136/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0924-0136(00)00611-7

to elliptical (e.g. Ponte Santa Trinita in Florence). Stone and brick cupolas based on a circle or a polygon appeared as an alternative construction solution (e.g. Santa Maria del Fiore in Florence). In the Baroque, Rococo and Neo-classicism the basic construction forms were not changed and only various ornaments and adornments were added. It was a complete change in the way of the perception of the world that has its roots in the Renaissance and then the Enlightenment that made civil engineering free from the enchanted circle of vertical pier and arch or double-curved roof. 2. Steel: basic construction material of the 19th and 20th centuries Steel and cement are two relatively new building materials that were introduced at the turn of the 18th and 19th centuries. First cast iron, then puddled and cast steel and ®nally re®ned and high strength steel proved to be very good construction materials. They are so-called ductile materials that have high tensile and compressive strength. This strength enables the construction of steel bent elements with spans that some years ago were beyond consideration. The subsequent improvements of the production technology made it possible to obtain steel with increasingly better properties. This progress is most easily seen when considering the steel bridges [1]: 1. Ironbridge (Coalbrookdale), England, arch bridge with upper deck (1779), 30.5 m span; 2. Telford's Bonar Bridge, Scotland, arch bridge with upper deck (1815), 45.7 m span; 3. Menai Bridge, Wales, suspension-chain bridge (1826), 176.4 m span; 4. Britannia Railway Bridge, Wales, box girder bridge (1850), 144 m span; 5. Clifton Suspension Bridge, England, suspension-chain bridge (1860), 214 m span; 6. Brooklyn Bridge, USA, suspension bridge (1887), 486 m span; 7. Forth Rail Bridge, Scotland, truss cantilever bridge (1889), 521 m span; 8. Sidney Bridge, Australia, arch truss girder with middle drive (1932), 504 m span; 9. George Washington Bridge, USA, suspension bridge (1931), 1067 m span; 10. Golden Gate Bridge, USA, suspension bridge (1937), 1280 m span; 11. Verazzano Narrows Bridge, USA, suspension bridge (1964), 1298 m span; 12. Forth Road Bridge, Scotland, suspension bridge (1964), 1006 m span (Fig. 1); 13. Tagus Bridge, Portugal, suspension bridge (1966), 1013 m span; 14. Alex Fraser Bridge, Canada, cable-stayed bridge (1986), 465 m span; Fig. 1. Forth Road Bridge in Scotland. 174 K. Flaga / Journal of Materials Processing Technology 106 (2000) 173±183

15. Queen Elizabeth II Bridge, England, cable-stayed bridge (1991), 450 m span; 16. Bosporus Bridge II, Turkey, suspension bridge (1988), 1090 m span; 17. New River George Bridge, USA, arch truss girder with upper drive (1978), 518 m span; 18. Humber Bridge, England, suspension bridge (1981), 1410 m span; 19. Pont de Normandie, France, cable-stayed bridge (1994), 856 m span (Fig. 2). Two suspension bridges have been constructed recently: the suspension Great Link Bridge with the span of 1624 m (®nished in 1998) in Denmark and the Akashi Kaikyo Bridge with the record span of 1990 m (®nished in 1998) in Japan. The Tatara Bridge, a cable-stayed bridge (®nished in 1998) with the record span of 890 m in this class of bridges, has been constructed in Japan. Despite such great progress, it seems that steel cablestayed bridges and suspension bridges are reaching the limits of their possibilities. The studio project of the bridge over the Messina Straits established that at the main span of 3000 m two pairs of cables with a diameter of 1.2 m (a mass of about 49.036 t/m) would be loaded mainly by their dead weight and not by the suspended deck with car and railway traf®c. That is the reason for a challenge for the engineering of the 21st century: what can the high strength steel cables be replaced to make them much lighter but as strong as the steel cables? Space engineering achievements, transferred to civil engineering, can be helpful. 3. Carbon ®bre reinforced polymer: a structural material of the future Application of CFRP (carbon ®bre reinforced polymer), the material that has been used until now in space and aviation techniques and professional sport, exempli®es this phenomena. EMPA Ð the Swiss Federal Laboratories for Materials Testing and Research in co-operation with the BBR, Stahlton and SIKA companies, are the pioneers in introducing this material to world engineering. CFRP is composed of very thin carbon ®bres with a diameter of 5±10 mm, embedded in polyester resin. The commercial carbon ®bres have the tensile strength of 3500±7000 MPa, an elastic modulus of 230±650 GPa and an elongation at failure ranging from 0.6 to 2.4 %. This material was ®rst applied in the strengthening of the Ibach Bridge near Lucerne in Switzerland in 1991 [2]. Laminated bands, size 150 mm1.75 mm or 150 mm 2.00 mm and 5000 mm long, glued to the reinforced zones were used there. The T3000 ®bres that form 55% of the laminated content, have a tensile strength of 1900 MPa and a longitudinal elastic modulus of 129 GPa. Today this technique of the strengthening of building structures is increasingly more often used. Fig. 2. Pont de Normandie over the mouth of Seine River, cable-stayed, span 856 m. K. Flaga / Journal of Materials Processing Technology 106 (2000) 173±183 175

In 1996 in Winterthur, Switzerland, the StorchenbruÈcke [3], a cable-stayed single pylon bridge of 124 m length, was built. Here the CFRP stay cables were applied experimentally for the ®rst time (Fig. 3). Each of the stay cables, consisting of 241 wires with diameter of 5 mm, interacts with conventional steel stay cables. The appointment of this small bridge for applying CFRP for the ®rst time was optimal as this material has practically zero thermal-expansion coef®cient. At a length of about 35 m, it does not cause any problems when used in co-operation with cables composed of different materials. The technical characteristics of the CFRP wires used in the stay cables mentioned above are as follows: T700 S ®bres, material density in the wires 1.56 g/m2 , ®bres content in the wires 68%, tensile strength 3300 MPa, longitudinal elastic modulus 165 GPa, thermal-expansion coef®cient 0.210ÿ6 Kÿ1 . From the above it follows that with very high resistance to axial tension exceeding even twice that of high tensile strength steel, the elastic modulus of CFRP stay cables is not much lower than that of the steel cables, whereas the mass density is about ®ve times lower. Therefore CFRP is the material of the future especially as it is durable, fatigue resistant, and non-corrosive. Before building in the CFRP stay cables used in StorchenbruÈcke, they were subjected to the test of 18.2 million load cycles at the stress amplitude of 220±270 MPa. The key problem that was faced was ®nding the method of anchoring the cables in the anchorage blocks. This was caused by the outstanding mechanical properties of CFRP being present in the longitudinal direction only. The anchorage system worked out by EMPA laboratory solved the problem by the use of a truncated cone shaped locking block ®lled with casting material, the mechanical properties of which change in accordance with the length of anchorage (Fig. 4). The main impediment to the widespread use of CFRP in civil engineering is the high price of carbon ®bres, at about 25 Swiss Francs per 1 kg (however, they are 5.2 times lighter than steel). Considering the time of exploitation of the Fig. 3. A cable-stayed bridge with one pair of CFRP cables and 11 pairs of steel cables for support. Fig. 4. Cone-shaped terminus of a 19-wire bundle encased in LTM (load transfer media). The inset shows the cross-sectional wire alignment (left) and the reduction in the epoxy coating thickness of the Al2O3 granules (right). 176 K. Flaga / Journal of Materials Processing Technology 106 (2000) 173±183

engineering object, the application of carbon ®bres may appear more reasonable economically. Finally, when referring to the question asked above, whether the CFRP stay cables may replace in the future the steel cables in suspension and cable-stayed bridges, it is worth quoting the data from paper [5]. The relative equivalent elastic modulus in steel cables decreases as their length increases from E 210 GPa when l 0, then E 163 GPa when l 1000 m to E 98 GPa when l 2000 m. The corresponding values for CRFP cables are 165, 163 and 162 GPa. These data and those above con®rm that for l > 2000 m CFRP cables may become a much appreciated material of the future for large-span engineering structures. 4. Concrete: basic construction material of the 20th century The other ``invention'' of the First Industrial Revolution that caused progress in civil engineering was cement. Socalled ``portland cement'' that was patented in 1824 by J. Aspdin proved to be an excellent hydraulic binder that was used for the production of a new material Ð concrete. This material is relatively cheap and easy to produce. Based on aggregates and water present in nature and using the cement mentioned above, it was possible to ``cast'' various shapes of elements and structures. Soon concrete became the most popular building material of the 20th century. As ``arti®cial stone'' it has the same disadvantages as natural stone: low tensile strength and high brittleness. It is true that the quotient of strength fctm/fcm is 1 10 for concrete (it is 1 26 for natural stones, according to Bauschinger) but nevertheless this enables concrete to be used for bending elements, i.e. for the arch or vault form, similarly to brick or stone structures that were dominating in the ®rst years of its application. It was only due to the successful attempts by Monier and Hennebique in the 1870s and 1890s that a valuable new building material called reinforced concrete was created. The strengthening of the tensioned zone in concrete elements by means of ¯exible reinforcing bars and very good co-operation of both materials in the construction, made possible the covering of a span ranging between 30 and 40 m with bent reinforced concrete elements. For larger spans, the dead load of the structure itself became dominant, thus determining the upper limit of application of reinforced concrete. The situation was similar to the case of the socalled tall buildings where the upper limit was a height of 20 storeys determined by the load capacity of the vertical elements such as walls and columns. Further progress was made possible owing to the introduction of active forces into concrete, i.e. prestressing of structure. Freyssinet's theoretical works and experiments (1926±1928) showed that for the prestressing procedure to be effective, high-strength concrete grades C30±C40 and prestressing steel with a strength of 1500±2500 MPa [6] must be used in the construction. Based on these assumptions, Dischinger built the ®rst prestressed bridge in Aue (Saxonia) in the years 1937±1938 whilst in 1938, Hoyer patented the method of prestressing by means of thin tendons that were tensioned before casting, and transferring the forces to the concrete through adhesion. In 1939±1940, Freyssinet patented the method of prestressing the hardened concrete using cables anchored at the ends of the element, the method still being in wide use. The introduction of prestressed concrete into civil engineering presented constructors with wonderful new opportunities (Fig. 5). There appeared new methods in the construction of bridges and public buildings (the cantilever and longitudinal sliding methods) as well as techniques (asymmetric shell structures, ribbon structures). The Varrod girder bridge in Kristiansand, Norway, was built in 1994 Fig. 5. Glen Jackson Bridge crossing the Columbia River in OR, USA. K. Flaga / Journal of Materials Processing Technology 106 (2000) 173±183 177