Review Question
Arch. 106 - Lecture Syllabus
Materials and Methods of Construction (3)
Professor Howard Weisenthal
0ffice: 21-214........Phone/Voice Mail: 756 2491........email: hweisent@calpoly.edu
CHAPTER 1: MAKING BUILDINGS
Answers to Questions in the Text
1. The members of a typical building design team are: a. The architect: Determines the form of the building, coordinates the design team, and takes the major responsibility for specifying and detailing the exterior and interior finishes. b. The structural engineer: Develops with the architect the design of the structural system of the building, and takes the major responsibility for calculating, specifying, and detailing the loadbearing structure, including cladding attachments. c. The mechanical engineer: Develops with the architect the design of the heating, ventilating, and cooling systems of the building (and often the plumbing system), and takes the major responsibility for calculating, detailing, and specifying these systems. d. The electrical engineer: Develops with the architect a design for artificial illumination of the building, and takes the major responsibility for calculating, detailing, and specifying this system, as well as systems of electric power distribution and communications wiring. e. The geotechnical and/or foundation engineer: Develops with the architect a design for the foundations and substructure of the building, and takes the major responsibility for calculating, detailing, and specifying this system. All these professionals are also involved in inspecting the construction work as it progresses, to be sure the specifications and details are followed, and to deal with questions that arise during construction. On many projects, a Construction Manager (CM) is also hired by the Owner of the building. The CM acts to coordinate the entire process of design and construction, and is often responsible for hiring the architect and engineers as well as the contractor and subcontractors.
2. The designers of a building must work under the existing physical constraints of a building site (size, shape, soil conditions, subsurface water conditions, vegetation, etc.), as well as legal constraints that include zoning ordinances, building codes, access standards, OSHA regulations, and energy efficiency standards. Additional constraints come from building insurance companies, building contractors, labor unions, and the client's program, taste, and budget.
3. Zoning ordinances control the type of use to which a piece of land may be put, how much of the land may be covered by buildings, how far the buildings must be set back from the property lines, how tall the building may be, how large a total floor area may be constructed on a given piece of land, how many parking spaces must be provided, and other such matters that have to do with the relationship of a building to its site and the community in which it is built. Building codes deal with questions of safety and health by controlling the quality of construction, especially with regard to structural stability and fire resistance, but also including space and light requirements, ventilation, emergency egress, and energy efficiency.
4. Fire resistance of building assemblies is measured in hours of fire endurance. Fire resistance is determined by subjecting a building assembly to a fire endurance test as specified by ASTM E-119.
5. If this building is not sprinklered, Types 1A, 1B, 2A, 2B or 4 construction are permitted; Types 2B and 4 are probably the most economical. If sprinklers are installed, Type 3A construction is also permitted.
Additional Questions
1. Name several organizations or types of organizations that publish construction information that is widely used by building professionals, and give an example of each. (Answer: ASTM, CSA, and ANSI publish standards for construction materials. Construction trade and professional associations publish technical information and technical standards. CSI and CSC publish Masterformat. Building materials manufacturers publish material concerning their products.)
2. What is Masterformat? Give titles of several of its primary divisions. (Answer: Masterformat is a standard outline for organizing information about construction materials and components. Its primary divisions cover such topics as Sitework, Concrete, Masonry, Metals, Wood and Plastics, etc.)
3. List several performance concerns, and several construction concerns, that are typically taken into consideration by a building professional. (Answer: Performance concerns include such things as fire, building movement, water vapor condensation, water leakage, acoustical privacy, deterioration, cleanliness, and building maintenance. Construction concerns include such matters as safety, schedule, budget, quality of work, division of work between the shop and the field, optimum use of trades, sequencing of operations, inclement weather, fitting of components, and quality assurance.)
4. What does a municipal building inspector have to do with new buildings? How does the inspector's work relate to zoning ordinances and building codes? (Answer: The building inspector receives applications for building permits, checks plans for conformance with building codes and zoning ordinances, issues building permits, and inspects construction to make sure it conforms to these standards.)
5. What types of publications would you consult to determine fire resistance ratings of various building components? Who publishes them? (Answer: Fire resistance ratings are tabulated in a variety of catalogs and handbooks issued by building material manufacturers, construction trade associations, and organizations concerned with fire protection of buildings.)
6. Define ASTM, CSA, CSI. (Answer: American Society for Testing and Materials, Canadian Standards Association, Construction Specifications Institute.)
True-False Questions
1. A building code contains off-street parking requirements. (F)
2. There is no limit in the building code on the height to which a Type 1A building can be built. (T)
3. First cost and life-cycle cost are the same thing. (F)
4. A single-family dwelling may be built of unprotected wood. (T)
5. In general it costs more to make a building more resistant to fire. (T)
Multiple Choice Questions
1. A zoning ordinance typically governs which of the following:
a. Types of activities that may take place on a piece of land
b. How much of the land may be covered by a building
c. How far a building must be set back from property lines
d. The maximum distance between exits in a building
e. Total floor area of a building on a given site
(Answer: a,b,c,e)
2. Fire resistance ratings for building components are given in units of:
a. Degrees Fahrenheit b. Degrees Celsius c. Hours d. Foot-pounds (Answer: c)
3. Access standards for buildings relate to:
a. Access from the street to the building for automobiles
b. Availability of an architect's drawings to the building inspector
c. Accessibility of all the electrical wiring and plumbing for inspection and repair the lifetime of the building
d. Access to a building by all members of the population, including the physically handicapped
Answer: d)
CHAPTER 2: FOUNDATIONS
Answers to Questions in the Text
1. The most common type of failure in foundations is differential settlement, in which overall settlement of the building is not excessive, but differences in the amount of settlement between different areas of the building cause failure of structural, cladding, or finish components of the building.
2. Fine sand consists of equidimensional particles that are large enough to behave as a particulate soil. Silt particles are also equidimensional but are much smaller, and silts are classified as fine-grained soils. Clay particles are even smaller than silt particles and are platelike rather than equidimensional. Unlike fine sand and silt, clay soils are governed in their properties by surface effects, and are therefore much more strongly affected by water content and the particular arrangement of particles in a given soil.
3. Sheeting may be by means of soldier beams and lagging, sheet piling, or slurry wall.
4. A watertight barrier is desirable in situations where lowering of the water table would have serious detrimental effects on neighboring buildings, and is possible in situations where the bottom edge of the barrier lies in an impermeable stratum of soil below the water table.
5. We use deep foundations in situations where competent soil lies too far beneath the surface to be reached by shallow foundations.
6. Belled caissons are practical only where the bell can be excavated from a cohesive soil, and where the bearing stratum beneath the bottom of the caisson is impervious to the passage of water.
7. Precast concrete friction piles have the largest potential loadcarrying capacity, followed by steel pipe piles, steel Hpiles, and sitecast concrete piles.
8. (The answer to this question is found in detail near the end of Chapter 2 of the text, under the heading "Designing Foundations").
Additional Questions
1. How do we know how much foundation load a soil can carry? (Answer: Building code tables such as Figure 2.5 give approximate bearing values for soils. For a more accurate determination, various laboratory tests and on-site tests may be conducted.)
2. What is the purpose of the slurry used in the process of constructing a slurry wall? (Answer: The pressure of the slurry against the walls of the trench prevents the walls from collapsing.)
3. When sheeting an excavation, which type of bracing is least obstructive to excavation operations? (Answer: Tiebacks.)
4. Why is it necessary to carry shallow foundations below the frost line? (Answer: If the soil beneath a foundation freezes, the foundation may be lifted by soil expansion or ice lenses.)
5. How does a driven pile transmit the load of a building into the soil? (Answer: By friction between the sides of the pile and the soil, by end bearing of the bottom of the pile against firm soil, or by both these means.)
True-False Questions
1. Wood piles may be used without a decay-preventive treatment if they lie totally beneath the water table. (T)
2. A waterstop is used to lower the water table in the vicinity of a building. (F)
3. Bentonite clay makes an excellent waterproof membrane around a basement. (T)
4. A slurry wall is a type of sheeting. (T)
5. A tieback must always be anchored in rock. (F)
6. The soil around an excavation can sometimes be stabilized by reinforcing it. (T)
7. Combined footings are used to save money in cases where concrete prices are high. (F)
8. Shallow footings may only be placed on undisturbed, natural soil. (F)
9. The foundation engineer need not be consulted by the architect and structural engineer until the size and position of the building on the land have been determined. (F)
Multiple Choice Questions
1. Which of the following are deep foundations: a. Caisson b. Strip footing c. Rock anchor d. End-bearing pile e. Mat foundation f. Friction pile (Answer: a,d,f)
2. Underpinning may include which of the following foundation types: a. Wall and column footings b. Piles c. Mini-piles d. Caissons (Answer: All of the above)
3. Which of the following are design thresholds that represent a major difference in the cost of a foundation? a. Building below the water table b. Building a slab on grade versus a crawlspace c. Using steel sheet piling versus concrete sheet piling d. Building close to an existing building e. Going from shallow to deep foundations (Answer: a,d,e)
4. Which of the following are cohesive soils: a. Cobbles b. Sand c. Clay d. Silt e. Peat f. Gravel (Answer: c)
5. Piles may be made from a. Timber b. Precast concrete c. Sitecast concrete d. Stone e. Steel f. Brick (Answer: a,b,c,e)
CHAPTER 3: WOOD
Answers to Questions in the Text
1. At the time a tree is cut, depending on the species of tree, the season of the year, and the amount of water present in the ground around the roots of the tree, its cells will contain a weight of water that is 30% to 300% of the dry weight of the cellulose and lignin. Assuming that the tree is immediately sawed into green lumber, each piece of lumber will then be seasoned by air drying or kiln drying. During this seasoning process, the free water contained in the hollow spaces of the cells is evaporated first, bringing the moisture in the lumber into the range of 26% to 32%. After the free water has evaporated, the bound water in the cell walls starts to evaporate, and the piece of lumber begins to shrink. Because radial shrinkage is not as pronounced as tangential shrinkage, each piece of lumber will also distort somewhat, the nature and degree of distortion depending largely on the portion of the log from which the piece was sawed and the orientation of the piece in the log. At a moisture content somewhere between 13% and 19% the piece is considered seasoned and can be installed in a building. After it is in place in the building, it will continue to lose water under very dry atmospheric conditions, and reabsorb water when the air is humid. This is usually best observed on a seasonal basis, with wood members of a building shrinking noticeably during a prolonged heating season, and swelling during a humid summer.
2. 3/4" X 3 1/2"; 1 1/2" X 3 1/2"; 1 1/2" X 5 1/2"; 1 1/2" X 7 1/4"; 3 1/2" X 3 1/2"; 3 1/2" X 11 1/4" if surfaced dry.
3. Wood is laminated to achieve a size, shape, or quality of piece that would otherwise be impossible.
4. Wood panel products are span rated; the first number in the rating (32) is the allowable span in inches between centers of rafters when used as roof sheathing, and the second number (16) is the allowable span when used as subflooring.
5. Pressure-treated wood might be specified for applications required increased resistance to fire, decay, or insects.
6. Redwood, Cypress, and various Cedars are the resistant species most common in North America.
Additional Questions
1. What are the advantages of quartersawn lumber? For what kinds of end uses would you specify it? (Answer: Quartersawn lumber is less prone to seasoning distortions, has a tighter grain figure, and has improved surface wearing qualities over plainsawed lumber. It is especially useful for flooring, interior trim pieces, and furniture stock.)
2. What grade of plywood veneer would you specify for a surface to be painted? For the backside of a sheathing panel? (Answers: A, D)
3. A variety of questions can be posed that require a knowledge of lumber dimensioning to solve. For example, you might show a detail of a foundation wall with a nominal 2" sill, 2X12 floor joists, and 5/8" plywood subflooring, and ask the student to figure the total actual distance from the top of the foundation to the top of the subfloor.
4. What will be the cost of 27 2X8s, each 14' long, if the price of the lumber is $240.00 per thousand board feet? (Answer: $120.96)
True-False Questions
1. The heartwood of a living tree is dead wood. (T)
2. Summerwood is stronger and stiffer than springwood. (T)
3. Box nails and common nails are Interchangeable in construction practice. (F)
4. Wood treated with pentachlorphenol can be painted. (F)
5. Sheet metal joist hangers are used to make a strong connection wherever wood joists bear on one another at right angles. (T)
Multiple Choice Questions
1. Which type of wood shrinkage is greatest? a. Longitudinal b. Radial c. Tangential
(Answer: c)
2. Which of the following are growth characteristics: a. Twisting b. Knot c. Check d. Decay e.Wane f. Cupping (Answer: b,d)
3 Lag screws are inserted with: a. A hammer b. A screwdriver c. A wrench d. A pneumatic gun (Answer: c)
4. Adhesives are widely used on the construction job site for: a. Laminating beams b. Connecting framing members c. Bonding the frame to the foundation d. Attaching subflooring and wall panels (Answer: d)
CHAPTER 4: HEAVY TIMBER FRAME CONSTRUCTION
Answers to Questions in the Test
1. Heavy timber framing receives relatively favorable fire ratings because large timbers catch fire and burn relatively slowly, and do not lose strength as quickly as unprotected steel members during a fire.
2. Where a wood beam joins a masonry wall, it must be protected against decay from moisture that may be present in the masonry, it must be anchored to the masonry so it cannot pull away, and it must be fastened in such a way that it can rotate out of the wall without damaging the wall if the beam should burn through during a fire.
Additional Questions
1. How is floor tilting due to wood shrinkage prevented in a building of Mill construction? (Answer: Columns are detailed so they do not bear on cross-grain wood at the floor lines. This is done either by using a single long column from foundation to roof, butting column sections to one another at floor lines with only steel plates between, or using iron pintle caps to transmit column loads through the floor structures.)
2. Explain why long laminated wood beams are often spliced between columns rather than at columns. (Answer: By splicing beams with hinge connections at points of zero moment, the bending action of each beam can be made fully continuous, which results in maximum structural economy by minimizing the size of the beam.)
True-False Questions
1. Two-inch framing members are permitted in the roofs of Heavy Timber buildings. (F)
2. Floor constructions in Heavy Timber buildings may not have any internal cavities. (T)
3. Finish flooring over the structural deck of a building of Mill construction is optional. (F)
4. All Heavy Timber buildings must have exterior masonry or concrete walls. (Fe-such walls are not required if there is sufficient space between buildings.)
Multiple Choice Questions
1. Wind uplift of the roof of a building of tradition Mill construction is counteracted by: a. Tying the roof beams together with iron dogs b. Using scuppers around the perimeter of the roof c. Using only heavy timber roof decking d. Running a steel anchor strap down the masonry wall from the end of each roof framing member (Answer: d)
2. Which of the following heavy timber frames must be buttressed or tied at the base to resist horizontal thrusts: a. Arch b. Continuous beam c. Rigid frame or portal frame d. Dome e. Truss (Answer: a,c,d)
CHAPTER 5: WOOD LIGHT FRAME CONSTRUCTION
Answers to Questions in the Text
3. In balloon framing the studs run in one piece from the sill to the rafter plate, while in platform framing the studs are interrupted by the floor platforms. Balloon framing has less vertical shrinkage from drying out of the wood, while platform framing is easier and safer to erect and is automatically firestopped, for which reasons it has become the method of choice.
4. Platform framing is automatically firestopped at each floor by the double top plate.
5. A wood beam under the ground floor of a platform frame will probably dry and shrink, allowing the floor to tilt, while a steel beam will not. A glue laminated wood beam is an acceptable substitute for a steel beam because it is made of thoroughly seasoned wood and will be fairly stable dimensionally.
6. A platform frame building is braced laterally either by let-in diagonal bracing at the corners, or by rigid sheathing such as plywood panels or diagonal boards.
7. A building code deals with the combustibility of platform framing in several ways. Most importantly, it restricts the height and size of such buildings, to keep occupant loads low and escape routes short. Escape of occupants is also facilitated by smoke and heat alarms, and bedroom windows of a size sufficient to permit the passage of occupants and firefighters. Building codes also encourage (and in many specific instances require) the protection of the wood frame with fire-resistant materials such as gypsum board or plaster, and sometimes with sprinklers.
Additional Questions
1. How is a platform frame anchored to a concrete or masonry foundation? (Answer: By means of anchor bolts embedded in the foundation, to which the sills are attached.)
2. Diagram in simplified fashion how a carpenter uses a framing square to lay out a common rafter and a hip rafter. (The answers can be extracted from Figures 5.47 and 5.51.)
3. What are the advantages and disadvantages of roof trusses as compared to conventional roof framing? (Answer: In many cases trusses are quicker to erect and use less material than the rafters and ceiling joists they replace. They can also span much farther than most conventional roof framing. In most cases, however, roof trusses are difficult to adapt to nonstandard or highly complex roof shapes, and they destroy most of the usefulness of the attic space.)
4. Sketch a floor framing layout for the plan shown, using joists spaced 16" o.c. [Furnish a plan that is not too extensive, but that does include a stair opening, cantilevered floor bays on two adjacent sides, and interior partitions in both directions.]
True-False Questions
1. A platform frame can be made entirely of nominal 2-inch lumber, plus suitable sheathing and subflooring materials. (T)
2. Foundations can be built entirely of wood. (T)
3. A foundation can be insulated either on the exterior or the interior. (T)
4. Wall frames are built in a horizontal position. (T)
5. The size of floor joists is independent of the species of wood used. (F)
6. Joist bridging is required by most codes. (F)
7. Subflooring runs under the sole plate in a platform frame. (T)
8. A rake is the same as an eave. (F)=
E. Multiple Choice Questions
1. Interior nonbearing partitions that run parallel to the floor joists can be supported by: a. Joist hangers b. Supporting studs c. Double joists d. Transverse blocking between joists c. Headers (Answer: c,d)
2. Studs that support two floors and a roof may be: a. 2 x 4, 24" o.c. b. 2 x 4, 16" o.c. c. 2 x 6, 24" o.c. d. 2 x 6, 16" o.c. (Answer: d)
3. A gable roof requires:, a. A ridge beam supported at intervals by columns or walls b. Ceiling joists to tie it against lateral thrust c. Either of the above d. Neither of the above (Answer: c)
CHAPTER 8: MASONRY
Answers to Questions in the Text
1. There are 3 syllables in "masonry." It should never be pronounced "masonerry."
2. The most common types of masonry units are bricks, concrete masonry units, and stone
.3. Mortar serves as an adhesive, holding masonry units together; as a cushion to create full bearing between units; as a sealant to keep weather from penetrating between units; and as a part of the finished surface of the wall.
4. Bricks and blocks are laid by processes that are very similar, but a brick is placed with one hand, while a block requires two.
5. Mortar joints are tooled to give a neat appearance of the desired type, and to compress the face of the mortar and make it more weathertight
.6. A structural bond ties two or more wythes of masonry into a single wall.
7. A cavity wall prevents penetration of water through a masonry wall by putting a continuous vertical airspace between the outer and inner wythes of masonry. When water reaches the cavity, it has no place to go but down. At the bottom of the cavity, the water is caught by a flashing and drained out through weep holes. (For cavity wall details see the illustrations in Chapter 8.)
8. Stone is laid differently than brick in that it is sometimes irregular and each piece must chosen and trimmed to fit; stones are often too heavy to lift by hand and must be lifted with lewises and hoists; mortar joints in fine stonework are raked out and later pointed with nonstaining mortar; and acids are not usedto clean many types of stonework.
9. External flashings should be installed at intersections of masonry walls with roofs or decks, to prevent penetration of water. Internal flashings should be installed wherever water might penetrate or accumulate inside a wall, such as over lintels and shelf angles, under copings and sills, at intermediate floors that bear on the wall, and at the base of the wall.
10. Weep holes should be provided just above each internal flashing, in the outside wythe of the wall. Their function is to drain water that accumulates over the flashing. They may be constructed by leaving out the mortar in head joints, laying short pieces of rope in mortar joints and then pulling them out, or by inserting plastic or metal tubes in the mortar.
11. Ordinary construction uses floors, roof, and interior walls of balloon frame construction, while Mill construction uses heavy timber framing for internal construction. The heavy timbers and decking used in Mill construction are slow to catch fire. Ordinary construction is usually protected with plaster or gypsum board over the wood components, and by firestopping between floors. Wood members bearing on the masonry walls in either system are firecut to prevent them from toppling the wall should they burn through in a fire.
Solutions to Exercises in Text
1. A restaurant is classified in Figure 1.1 as Type A-3, Assembly. In Type 4 construction, the building would be limited to 3 stories or 40' of height, with a maximum of 12,600 square feet per floor--but because the building is more than 2 stories high, Figure 1.2 tells us that we must reduce the allowable floor area by 20%, which comes out to 10,080 square feet per floor. In Type 3B construction, these figures drop to 2 stories, 30', and 8,400 square feet, respectively. If unprotected steel joists are substituted for the wood joists, the construction type becomes 2C, but the figures remain the same as for unprotected Ordinary construction. If precast concrete plank floors with a fireresistance rating of 2 hours are used, the building becomes incombustibles By looking in the chart in Figure 1.3, line 11, we see that incombustible buildings with 2 hour floor construction are classified as Type 1B construction. Returning to the chart in Figure 1.1, we find that our masonry restaurant building with precast concrete plank floors would have no limitations on height or area
.2. This wall will consist of 17 blocks and 16 mortar joints. Its length will therefore be 16 times 16", plus the last block at 15 5/8". This adds up to 271 5/8", or 22'-7 5/8".
3. This opening is equivalent to 4.5 blocks at 16" of length each, plus one mortar joint of 3/8". This works out to 72 3/8", or 6'-0 3/8".
4. 44 courses times 8/3 inches per course equals 117 1/3", or approximately 9'-9 3/8".
Additional Questions
1. What are the components of modern masonry mortar? (Answer: Portland cement, lime, fine aggregate (sand), and water.)
2. What are the major molding processes for clay bricks? (Answer: water-struck and sand-mold, which are hand molding processes, and dry-press and stiff mud, which are machine molding processes)
.3. Sketch an elevation view of a portion of a brick wall laid in running (or common, English, Flemish) bond. t answer: see Figure 8.17).
4. What are the three major types of building stone? (Answer: sedimentary, metamorphic, igneous) Give an example of each. (Answers: Sedimentary--sandstone, limestone, travertine; Metamorphic--marble, slate; Igneous--granite.)
5. What is the usual way of adding vertical and horizontal steel reinforcing to a concrete masonry wall? (Answer: vertical reinforcing bars are grouted into the hollow cores of the masonry units at the desired intervals, and horizontal joint reinforcing made of very thin steel bars is laid into the bed joints of mortar at the desired intervals.)
6. What is the chief reason to build a masonry cavity wall? (Answer: A cavity wall is much more resistant to the passage of water than a solid wall. Additionally, a cavity wall may be thermally insulated by adding slabs of plastic foam insulation within the cavity.)
7. Sketch a detail section of the base of a cavity wall with a brick facing and an 8" concrete block backup. Label all the parts.
True-False Questions
1. Quicklime is mixed with Portland cement, sand, and water to make mortar. (F)
2. Masonry units should always be wetted before laying. (F. under most conditions units should be laid without wetting).
3. Bricks shrink considerably during firing. (T)
4. There is no truly standard brick size. (T)
5. Mortar color is of little consequence to the finished appearance of a brick wall. (F)
6. Flemish bond is purely decorative. (F)
7. It is possible to build a brick dome without using formwork. (T)
8. It is almost impossible to build brick walls that contain steel reinforcing bars. (F)
9. Limestone is easily cut just after it is quarried, but becomes harder with age. (T)
10. Ashlar stone is very irregular. (F)
11. Marble work should be cleaned with muriatic acid after the mortar has hardened sufficiently. (F)
12. There is no truly standard size of concrete block. (F)
Multiple Choice Questions
1. Portland cement mortar that is growing hard before use may be retempered with water and used: a. within 30 minutes of its mixing b. within one hour of its mixing c. within 90 minutes of its mixing d. within a half day of its mixing e. within a day of its mixing (Answer:c)
2. The most standard mortar joint thickness is:
a. 1/8" (3.2 mm) b. 1/4"(6.4 mm) c. 3/8" (9.5`mm) d. 1/2"(12.7 mm)
e. 5/8"(15.9 mm) (Answer: c)
3. Which of the following mortar joint profiles are appropriate use outdoors in a severe climate: a. weathered b. concave c. vee d. flush
e. raked f. stripped g. struck (Answer: b,c)
4. Type I (moisture-controlled) concrete masonry units should be specified:
a. Where appearance is important
b. In damp weather
c. For underground work
d. In severe climates
e. Where shrinkage of a wall must be controlled
(Answer: e)
5. Movement joints should be located in masonry walls:
a. at discontinuities where cracks would tend to form
b. every fourth course
c. every sixth course
d. every seventh course
e. at a change of brick bond
(Answer: a)
6. Internal flashings should be located in masonry walls: a. below copings and sills b. above lintels and shelf angles c. below lintels and shelf angles d. at the base of the wall e. every sixth course (Answer: a,b,d)
CHAPTER 9: STEEL FRAME CONSTRUCTION
Answers to Questions in the Text
1. Steel is any of a range of iron alloys that contain less than 2% carbon, while iron may contain a larger proportion of carbon.
2. Steel structural shapes are produced by passing steel between rollers while it is still hot enough to be formed easily. The different weights and thicknesses of a shape are produced by varying the spacing between the rollers.
3. The fabricator receives steel shapes from the mill and prepares them for specific building frame by cutting them to length, punching or drilling connector holes as required, adding connecting angles and plates, and cambering and priming the components as required. The erector receives these prepared building parts from the fabricator and assembles them on the building site.
4. A W21 X 68 is a wide-flange steel section nominally 21" in depth and weighing 68 pounds per linear foot.
5. In a moment connection, the flanges or a beam or girder are attached to the adjoining member with welds (or, rarely, with bolts) that are as strong as the flanges themselves. One member cannot rotate without rotating the other member. In a shear connection, the welds or bolts are designed to transmit only the vertical load from the beam or girder to the adjoining member, and small rotations are possible between the two members. Moment connections are used for joints that must be made rigid to contribute to the overall rigidity of the building, or to create structural continuity between members. Shear connections are less expensive than moment connections and are used for all other connections.
6. The top flange of a beam is often coped so its top surface can lie in the same plane as the top of a girder to which it is connected. The bottom flange is coped in a knife connection to allow the beam to be inserted between the connecting angles by sliding it in from above.
7. Composite construction allows a steel beam or deck and the concrete fill above to act together as a single structural unit, which allows the use of a lighter steel member than would otherwise be the case.
8. Steel is advantageous in a fire because it is incombustible and does not contribute fuel to the fire as a wood beam does. Steel does, however, lose much of its strength at elevated temperatures, so must be protected by incombustible materials that will insulate it from the high temperatures of a fire.
9. Trusses, dome, arches, cable net structure, space truss
.Answers to Exercises
3. A department store is classified as Use Group M, Mercantile. Assuming it has no automatic fire suppression system, we see from the table in Figure 1.1 that the lowest type of construction that might permit a four-story building with 17,500 square feet per floor is Type 2A, but we must correct the allowable area per floor (22,800) with a 10% adjustment for a four-story building as specified by Figure 1.2. This gives 20,520 square feet per floor, which is greater than the 17,500 we wish to build, so Type 2A construction will suffice. Moving to Figure 1.3, we can now determine on line 9 that lower-floor columns must have 2-hour protection, on line 11 that floor beams must be 1 1/2 hours, roof beams (line 12) must be 1 hour, and walls around shafts and stairways (lines 5 and 6) must be of 2-hour construction.
Additional Questions
1. Why are the edges of steel members beveled in some cases before welding? (Answer: A beveled edge allows access for the welding electrode so multiple passes can be made to fill the joint with weld metal to the same thickness as the member being connected).
2. What is the difference between an AISC Type 1 connection and an AISC Type 2 connection? (Answer: The Type 1 is a moment connection, and the Type 2 is a shear connection.)
3. Where is a seated connection likely to be used, and why? (Answer: A seated connection is used to connect a beam or girder to a column web, because it allows better access for pneumatic wrenches in this restricted location than does a framed connection.)
4. In what circumstance is a butt plate used in a column-to- column connection? (Answer: Where the column changes from one nominal size of section to another.)
5. Why are columns spliced at waist level above the floor? (Answer: This avoids conflict with beam-column connections, and is convenient for the ironworkers to reach.)
True-False Questions
1. Most steel beams are I-beam shapes. (F)
2. Open-web steel joists are made by cutting the web of a wide-flange section along a zig-zag path, then rejoining the two halves in a greater depth by welding. (F)
3. Riveting of steel building frames is obsolete. (T)
4. In slip-critical connections, the bolts grip the two steel components so tightly together that the load is transferred between them by friction. (T)
5. Plumbing-up refers to the process of raising sections of steel from the ground to their position in the building. (F)
6. Column baseplates for smaller columns are usually attached to the columns in the fabricator's shop. (T)
7. Plate girders are available from stock in a variety of sizes and spans. (F)
8. Rigid frames are economical for low-cost manufactured steel buildings. (T)
9. Tensile structures made of steel cables can be made rigid against wind uplift. (T)
F. Multiple Choice Questions
1. Steel structural`: shapes are produced by: a. casting b. forging c. die- forming d. rolling e. milling (Answer: d)
2. The width of the flange of a W12 X 14: a. is 12" b. is 14"
c. is the standard 6" dimension used for all W sections d. is up to the mill that produces it e. must be looked up in a handbook (Answer: e)
3. Mild structural steel is designated by the ASTM number of:
a. A36 b. A242 c. A441 d. A572 e. A588
(Answer: a)
4. The following materials are good for fireproofing steel columns:
a. Concrete b. Brickwork c. Metal lath and plaster d. Gypsum board e. Spray-on fireproofing
f. Mineral fiber slabs g. Intumescent coatings
(Answer: all of the above)