Why That Building Looks Like That

Questions

1. 1
   Not answered. A steel bridge span is 45 meters long when it is installed. Steel's linear thermal expansion coefficient is about 12 × 10⁻⁶ per °C. If the temperature rises by 30°C, about how many millimeters longer does the span become?
2. 2
   Not answered. A building has expansion joints in its facade panels, its floor slabs, and its parapet coping. What job do all three shapes of joint share?
3. 3
   Not answered. Concrete slabs almost always crack eventually as they shrink while curing and then expand and contract with temperature. What does cutting a shallow control joint into the surface accomplish, if it cannot stop the slab from cracking?
4. 4
   Not answered. Why is a sidewalk's control-joint groove cut only shallowly into the surface, instead of all the way through the slab?
5. 5
   Not answered. Which statements correctly explain why a very long brick wall needs a vertical movement joint somewhere along its length, while a short garden wall usually does not?
6. 6
   Not answered. A homeowner notices a crack in a plastered wall. Which description should prompt an immediate call to a structural engineer rather than a routine repaint?
7. 7
   Not answered. Why is an expansion or movement joint filled with a soft sealant or compressible foam instead of being pointed up with ordinary mortar?
8. 8
   Not answered. Along the bottom course of a brick veneer wall, small gaps are left in the mortar every couple of feet instead of pointing them solid. What are these gaps for?
9. 9
   Not answered. In a rain screen wall system, what does keeping the cavity behind the outer cladding vented to the outside air mainly accomplish?
10. 10
    Not answered. Flashing is a thin, sloped strip of water-resistant material installed above a window or door opening in a wall. What typically happens if it is installed backward — sloped inward toward the building instead of outward — or omitted entirely?
11. 11
    Not answered. A window sill has a thin groove cut into its underside, a few millimeters back from the outer edge. What does this drip groove actually stop?
12. 12
    Not answered. Two identical buildings sit side by side. One has generous roof overhangs; the other has none. After ten years, which one is more likely to show heavy vertical streaking on its walls, and why?
13. 13
    Not answered. A white, powdery bloom appears on the surface of an exterior brick wall. What is efflorescence actually telling you about the wall?
14. 14
    Not answered. In cold climates, why does saturated masonry or concrete paving tend to flake and crumble at its surface after repeated winters, even without any change in load?
15. 15
    Not answered. In traditional masonry, mortar is deliberately made softer and weaker than the brick or stone units it holds together. Why is that the goal, rather than a compromise?
16. 16
    Not answered. Why can repointing old, soft-lime brickwork with modern, hard Portland cement mortar actually accelerate damage to the brick, instead of fixing the wall?
17. 17
    Not answered. The coping stones or metal caps along the top of a parapet wall are almost always installed with a slight slope and an overhanging drip edge, rather than sitting perfectly flat and flush. Which statements correctly explain why?
18. 18
    Not answered. Concrete is strong in compression but weak in tension, so steel reinforcing bars are placed wherever tension is expected. In a simply supported beam that sags under load, and in a cantilever that projects from a single support, where does the rebar mostly sit?
19. 19
    Not answered. Building codes specify a minimum thickness of concrete, called cover, between the outer surface of a concrete member and the reinforcing steel inside it. Why is too little cover classified as a durability problem rather than a strength problem?
20. 20
    Not answered. A parking garage ceiling has a patch of concrete flaking away, revealing rusted rebar underneath. What mechanism is directly responsible for pushing that chunk of concrete off?
21. 21
    Not answered. Which environments tend to make reinforced concrete structures deteriorate fastest, and why?
22. 22
    Not answered. How does carbonation, the slow reaction between carbon dioxide in the air and concrete, eventually lead to reinforcing steel corroding, even without any chloride exposure?
23. 23
    Not answered. A concrete beam shows a thin, reddish-brown streak running down its face from a hairline crack, with no visible spalling yet. What does that stain most likely indicate to an inspector?
24. 24
    Not answered. On the face of some concrete parking structures and bridge decks, a regular grid of circular or square patches is visible, slightly different in texture from the surrounding concrete. What do these patches typically mark?
25. 25
    Not answered. On the ceiling of an older building, faint dark lines sometimes appear running parallel to hidden structural elements below the surface, like joists or slab edges. What causes this pattern, sometimes called ghosting?
26. 26
    Not answered. Modern glass office towers often have windows with a faint blue, green, or bronze color cast when viewed from outside, even though the glass looks clear from indoors. Which statements correctly explain this?
27. 27
    Not answered. On a glass curtain-wall tower, the vision glass at each floor is bordered above and below by an opaque strip of glass or metal in roughly the same color family. What is behind that opaque strip?
28. 28
    Not answered. Why do many modern facades include a visible horizontal shadow gap or reveal at each floor line, rather than a perfectly flush surface from top to bottom?
29. 29
    Not answered. In older, pre-steel-frame masonry buildings, the walls are often noticeably thicker at the ground floor than near the roof. Which statements correctly explain why?