Öngerilmeli beton ve çelik gemilerin ekonomik açıdan karşılaştırılması
Comparison of prestressed concrete and steel ships from economical point of view
- Tez No: 39783
- Danışmanlar: PROF.DR. MESUT SAVCI
- Tez Türü: Doktora
- Konular: Gemi Mühendisliği, Marine Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1994
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 150
Özet
ÖZET Öngerilmeli beton, betonun yük altında oluşması muhtemel çekme gerilmelerine eşit miktarda beton içindeki yüksek mukavemetli çelik teller, halat veya çubukların çekmesinden kaynaklanan sürekli basınç gerilmelesıne tabı tutulmasıyla elde edilir. landon olarak tanımlanan bu çekilmiş çelik genellikle çekilmemiş donatı ile birlikte kullanılır. Ongenime!i beton, kriyojenık depolama için ilk olarak 1952 ve 1953 yıllarıda sıvı oksijenin depolanması için yapılan iki Öngerilmeli beton tankda kullanılmıştır. Bu çalışmada, öngerilmeli beton duba ve gemilerin teknik ve ekonomik özellikleri incelenmiş ve çelik duba ve gemilerle karşılaştırılmaya çalışılmıştır. Yapılan kabuller ve hesaplar, öngerilmeli beton dubaların çelik dubalara göre daha ekonomik olduğunu, öngerilmeli beton gemilerin ise boyutlar arasındaki oranların dikkate alınmaması halinde veya boyut kriterleri esas alındığında seri üretim yoluyla kalıp giderlerinin azaltılması, çelik gemilerin boyanması sırasında çalıştırılmaması gibi etkenlerden dolayı bazı durumlarda çelik gemilerden daha ekonomik ola¬ bileceğini ortaya koymaktadır.
Özet (Çeviri)
COMPARISON OF PRESTRESSED CONCRETE AND STEEL SHIPS FROM ECONOMICAL POINT OF VIEW SUMMARY Prestressed concrete can be obtained by subjecting concrete to a permanent compressive stress, caused by tensioning high-tensile steel wires, strand ör bars anchored to the concrete of the same order of mağnitude as the tensile stress expected to occur under load. Thls tensioned steel, referred as tendon, is generally used with normal reinforcing steel. The tendons may be tensioned before placing concrete and the tension released after the concrete has set. This process is known as pretensioning. in another way, the concrete may be cast and the tendons, arranged either outside the concrete ör lying ducts, tensioned when the concrete has attained adaquate strength. This process is known as post-tensioning. Utilization of local materials, ease in construction, less initial and maintenance cost and especially it is the only material normally used at ambient temperature conditions that can also be used at cryogenic temperatures make prestressed concrete ideally suited for a variety of applications in the area of storage and transportation of liquefied gas. Since prestressed concrete was first used for storing of liquid oxygen, this material has finally been accepted and used. Prestressed concrete for cryogenic storage was first used in 1952 and 1953 for two prestressed tanks for storing of liquid oxygen. When compared with steel, slower thermal response of concrete, makes it a beneficial protective material. xiiThe aim of this study is to compare steel with prestressed concrete used as barges and ships and eyaluation of each from technical, economical and other aspects. Studies made on several concrete ships have shown that, concrete compared with steel has advantages from behavioral and economical point of view. Behavioral advantages can be listed as follows: 1.Saving in maintenance, 2.Durable, 3.Materials can be obtained easily, 4.Greater strength to impact and accident conditions, 5.Less time consuming in case of damage, 6.Easily formed to complex curves, 7.Incombustibility, 8.Good insulation characteristics. in order to compare prestressed concrete and steel ships from economical point of view first, a simple barge is selected. Assuming that the barge's load capacity ıs 4000 tons, with varyıng lengths between 50-100 m and depths between 6-13m, the width, weight and cost of prestressed concrete barge is calculated. The calculations of stili water bending moments and wave induced bending moments are made using the rules given by Ameri can Bureau of Shipping. The unit costs of ste¬ el and prestressed concrete are calculated as 13000 TL/kg (excluding painting) and 4.246.141 TL/m3 (including formwork) respectively with 1993 prices. Then, using a computer program the barges with a load capacity between 4000-10000 tons are examined and results are tabulated and shown with graphs. The same procedure is used för steel barges and comparisons are made. xi i iFrom graphs, for the loads between 4000-10000 tons of barges made from both materials fo11owings are evaluated: a)There exist similar relations between their lengths-depths and related to these their widths. b)in steel barges, depending on increasing length and depth, widths are decreased, whereas in prestressed concrete barges, upto 6,7 and 8 meter depths parallel concrete barges, upto 6,7 and 8 meter, depths parallel to the lengths, widths are increased. c)in a similar manner, depending on length when compared to steel, concrete barge weights are extremely increased and relation is constant when depth is increased. d)The relations between width and weıght with length-depth are also valid for initial costs. The study made for comparison of prestressed barges with steel barges is also applied to ships by changing coefficients. For this purpose, C. and C are accepted as 0.70 and 0.80 respectively and cost çal çul ati ons are made accordingly. Considering the annual incomes and disbursements, annual eguivalent amount of prestressed concrete and steel ships of different ships made of both materials are assumed to have a useful life of 20 years with no salvage value. it is considered that the annual equivalent amounts of ships are variable according to unit costs per ton-mile, annual usage of ship capacities, time required handling and. rehandling in harbours and unit freight rates per ton-mile depending on supply and demand in world market, in order to make comparison, it is assumed that the ships work 330 days a year vnth ful! capacities and yearly net profit is 10%. xiVin order to determine annual incbmes and costs, to make comparison, dally freight rate and unit cost for displacement are çal cırt ated by taking, the ships of 50 m length, 6 m depth with 4000 tons capacity and 100 m length, 13 m depth with 10000 tons capacity, into account as extreme two cases. Calculations show that in order to provide above assumptions, the unit cost per ton of dispalacement and freight rate per day should be 0.32 $ and 1.23 $ respectively. Since, steel ships need to be painted against corrosion, p approximately 6$/m painting cost is considered accepting that ships are painted every 4 years. in cash flow diagrams, the initial costs and annual incomes and costs calculated with Turkish Lira (TL) are changed to U.S. Dollars, accepting that l U.S. Dollar is equal to 10000 TL with 1993 prices and Libor = 7% as annual interest rate. ' in case that the proportions between dimensions are not considered some prestressed concrete ships seem to be more economical than steel ships. But, if the Length/Depth ratio is accepted to be between 9 and 14 than, ali steel ships become more economical. in the study, prestressed concrete and steel ships of different dimensions are also compared. For this purpose, a different width for each length is selected and load capacities, weights, initial costs and annual costs of prestressed concrete ships compared to steel ships are calculated for different depths. in determining width and depths depending on lengths, the minimum ratios between dimensions are considered and Length/Width>3, Width/Depth>1.5 are accepted. The results show that: a) For ali length and widths. Load capacities of steel and concrete ships, depending on depths, increase linearly and the effect xvof depth to load capacity is more in concrete ships than steel ships, b)For ali lengths, rate of initial costs of concrete ships, depending on depths, increase more than steel ships, c)Annual costs of concrete ships are about 83% of those of steel ships. Generally, in ships if the Length/Depth ratio decrease and Length/Width ratio increase the annual costs decrease. This shows that, among the ships having same Length x Width x Depth, increasing depth instead of width makes the ship more economical. The annual equivalent amounts of prestressed concrete ships will increase than those calculated in the study when it is considered that the construction period of concrete ships is less than that of steel ships, they have more useful life and by mass production less initial cost due to formwork. in order to provide economy in prestressed concrete ships against conventional steel ships, there are several aspects. Öne of those, structural design, not only affects the cost but also weight which is very important from different views. it is concluded that, prestressed concrete may be used more economically than steel in barges for short distances ör where the transportation capacity is not important and speed is negligible. Prestressed concrete may also be used in LPG ships where safety is more important than economy. in order that, concrete ships are to. compete with steel ships for long distances, designs are to be made to minimize weight and maximum possible concrete and workmanship quality are to be provided. For this purpose, it will be more benefical that ship and civil engineers work together with class societies. xvi
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