Concrete Capacity Design

ACI 349.2R-07, Guide to the Concrete Capacity Design (CCD) Method -Embedment Design Examples, American Concrete Institute Farmington Hills, MI. 

Fuchs W., R.Eligehausen, and J. Breen (1995), Concrete Capacity Design (CCD) Approach for Fastening to Concrete, ACI Struetural Journal, Vol. 92, No. 1, American Concrete Institute Farmington HiUs, MI. 

The basic theory behind conventional reinforced concrete beam design is well known. Essentially, steel reinforcement is placed near the bottom of the beam and is used to carry the tensile stresses while the concrete at the top of the beam carries the compressive stresses. To avoid failure of this concrete in compression, the steel is actually underdesigned so that it will fail first. Thus, the concrete never reaches its ultimate capacity (5). 

This apparently undesirable behavior is deliberately taken into account by the modem strategies for aseismic design of reinforced concrete structures, based on the concept of the capacity design, as it allows the reduction of the inertia forces acting upon the stmctures by means of energy dissipation. 

Eurocode 8 (EC8) follows three general design concepts based on the ductiUty requirements and capacity design considerations of steel buildings the concept of the low-dissipative structural behavior of DCL structures, the concept of dissipative stmctural behavior of DCM and DCH stmctures satisfying the ductility and capacity design requirement, and the concept of dissipative structural behavior with steel dissipative-controUed zones. In the latter case, when composite action may be considered from Eurocode 4 (EC4) in the presence of the steel and concrete (slab) interaction, specific measures have been stipulated to prevent the contribution of concrete under seismic conditions, hence apply general rules for steel frames. 

Furnace Design. Modem carbide furnaces have capacities ranging from 45,000 t/yr (20 MW) to 180,000 t/yr (70 MW). A cross-section of a 40 MW furnace, constmcted in 1981, having a 300 t/d capacity is shown in Figure 2. The shell consists of reinforced steel side walls and bottom. Shell diameter is about 9 m and the height to diameter ratio is shallow at 0.25 1.0. The walls have a refractory lining of 0.7 m and the bottom has a 1-m layer of brick topped by a 1.5-m layer of prebaked carbon blocks. The steel shell is supported on concrete piers and cooling air is blown across the shell bottom. A taphole to withdraw the Hquid carbide is located at the top of the carbon blocks. 

A drainage ditch is to be built to carry rainfall runoff from a subdivision. The maximum design capacity is to be 1 million gph (gal/hr), and it will be concrete lined. If the ditch has a cross section that is an equilateral triangle (open at the top) and if it has a slope of 2 ft/mi, what should the width at the top be ... 

Direct Shear. For type I cross-sections (0 < 2°) the concrete between the flexural reinforcement Is capable of resisting direct shear. However, because cracking at the support yield line reduces the shear capacity, diagonal bars must be provided to at least resist the shear capacity of the concrete, v. For type II and III cross-sections (0 > 2 ), with little or no concrete shear resistance, The diagonal reinforcing bars must be designed to resist the entire shear load at the support. 

Limit state design methods are used in blast resistant design. These methods provide a comprehensive, reliable and realistic means of predicting failure mechanisms and structural capacities. Limit state design methods for structural steel, cold formed steel, reinforced concrete and reinforced masonry are available. However, as of now, no similar design specification is available for aluminum structures. 

Connections must be sized to transfer computed reaction forces and to assure that plastic hinges can be maintained in the assumed locations. For reinforced concrete design, splices and development lengths are provided for the full yield capacities of reinforcing. For structural steel design, connections are designed for a capacity somewhat greater than that of its supported member. Further information is provided in later sections of this chapter. Typical connection details are provided in Chapter 8. 

The primary failure mechanisms encountered in reinforced concrete buildings arc flexure, diagonal tension, and direct shear. Of these three mechanisms,. flexure is preferred under blast loading because an extended plastic response is provider prior to failure. To assure a ductile response, sections are designed so that the flexural capacity is less than the capacity of non-ductile mechanisms. 

This chapter presents an overview of various details applicable to blast resistant structures. Many details for conventional steel and concrete structures, and specific details for seismic design, are applicable to these structures and are not included. Details should meet the requirements of design capacity, energy absorption, and ductility. 

The liquid waste is stored for at least 6 y prior to solidification to reduce the decay heat (Fig. 16.8) by a factor of 10 or more. The first U.S. military fuel reprocessing wastes were stored as neutralized waste in mild steel tanks at the Hanford reservation in eastern Washington. These steel-lined, reinforced-concrete tanks were 500,000-1,000,000 gal in capacity with provisions for removal of waste heat and radiolysis products. Corrosion of several tanks occurred with the release of waste. Fortunately, the soil around these tanks retarded nuclide transport. A better (and more expensive) design for storage tanks was implemented at the Savannah River site in South Carolina consisting of a second steel tank inside of a Hanford-style tank. The storage of acid waste in these tanks has not encountered the corrosion problems seen with the Hanford tanks. 

Natural-draft cooling towers with a hyperbolic configuration are usually constructed of concrete, have a large dimension and, consequently, large capacities. They are generally used in power plants. Figure 4.3 also illustrates this design. 

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