Blog Archives

What’s in My Walls?

Posted by on 16/ 11/ 15

The first step to determining your upgrade options is to learn the type and amount of insulation, if any, in your walls. Houses built before 1930 often were left uninsulated, so you will find either empty stud bays or insu­lation that was added later. Houses built in the ’40s, ’50s, and beyond typically were in­sulated, but often with thin batts that didn’t fill the wall cavity.

The possibilities shown here represent the most common types of early insulation, but it’s not a comprehensive list. Many of the earliest forms of insulation were driven by the local industry. If the town was home to sawmills, the surrounding houses could be insulated with sawdust. If the town was an agricultural hub, rice hulls were fairly com­mon...

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HEADERS

Posted by on 16/ 11/ 15

Every opening in a wall must have a header over it. Headers must be able to carry a cumulative load and transfer it downward without warping, flexing, or pulling away from the sides of the opening. Thus headers must be sized according to the loads they carry and the distances they span. Your local building code will have the final say in sizing them.

That noted, many builders in North America use this rule of thumb when sizing headers for single-story buildings with 2×4 walls and a 30-lb. live load on the roof: The nominal depth a 4 x header in inches equals the span in feet of the opening. For example, if a builder uses No. 1 grade Douglas fir on edge, its spans look like this:

Douglas Fir Header Spans

HEADER SIZE (in.)

SPAN (ft.)

4×4

4

4×6

6

4×8

8

4×10

10

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Exploring Your Options

Posted by on 16/ 11/ 15

To assess the framing hidden behind finish surfaces, go where it’s exposed: the basement and the attic. Joists often run in the same direction from floor to floor.

Generally, a girder (also called a carrying timber or beam) runs the length of the house, with joists perpendicular to it. Some houses will have framed cripple walls (short walls from the top of a foundation to the bottom of the first-floor joists) instead of a girder. Main bearing walls often run directly above the girder, but any wall that runs parallel to and within 5 ft. of a girder or cripple wall is probably bearing weight and should be treated accordingly.

Bearing walls down the middle of the house are also likely to be supporting pairs of joists for the floors above...

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CONCRETE BRIDGE DECK CONSTRUCTION

Posted by on 16/ 11/ 15

During construction, bridge deck concrete can be supported by reusable wood forms, permanent stay-in-place steel forms, or precast prestressed-concrete planks. Where per­mitted, contractors will generally use stay-in-place steel forms rather than removable wood forms. Allowance must be made in the design of the bridge for the extra weight of the steel forms, and for extra concrete where required. The forms are corrugated. Where the bottom transverse bar spacing can be made the same as the pitch of the corrugated form, the extra concrete in the valley below the nominal bottom of the slab line is com­pensated for by the concrete displaced by the peak of the corrugation above the bottom of the slab line, and the allowance can be for the weight of the forms only...

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CONCRETE BRIDGE DECK DESIGN

Posted by on 16/ 11/ 15

AASHTO Standard Specification requirements for design of concrete bridge deck slabs on longitudinal beams are based on distribution of loads in the slab according to Westergaard theory and assume flexural action of the slab. On the basis of these specifica­tions, many states have developed design tables and charts for quick determination of slab thickness and both primary (transverse) and secondary (longitudinal) reinforcement. The main variables in the design of the deck slab are

• Beam spacing

• Concrete strength

• Weight allowance for future paving

• Live load (generally HS 25 or, LRFD, HL-93)

• Continuity factor for dead load

Applying the specifications, the simple dead and live load moments per unit width of slab are calculated...

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Graphic Approach

Posted by on 16/ 11/ 15

Once the data series is identified and ranked and the plotting position is calcu­lated, a graph of magnitude x versus probability [P(X > x), P(X < x), or T] can be plotted and a distribution fitted graphically. To facilitate this procedure, it is common to use some specially designed probability graph paper rather than linear graph paper. The probability scale in those special papers is chosen such that the resulting probability plot is a straight line. By plotting the data using a particular probability scale and constructing a best-fit straight line through the data, a graphic fit is made to the distribution used in constructing the prob­ability scale. This is a graphic approach to estimate the statistical parameters of the distribution.

Example 3...

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Begin with door and window assemblies

Posted by on 16/ 11/ 15

I begin framing by building the door and window assemblies. All window headers and most door headers need top cripples (sometimes called jacks) and all rough sills need bottom cripples (see the illustration on the facing page). A chopsaw worker has probably already cut these to size and grouped and labeled them. Grab an armload and carry them to their proper locations. Check to see that the cripples match the lengths written on each header. Every header takes a cripple on each end and one on each layout mark. Pay close attention! Place bottom cripples perpendicular to the wall plates, exactly where they will be nailed in place. I also place a trimmer and a king stud next to each window opening before I do any nailing.

To make toenailing cripples to headers easier, back up the cripple with ...

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Bracing

Posted by on 16/ 11/ 15

Tumbleweed would have to withstand not only the normal wear and tear of everyday living, but also the occasional jolts and gale-force winds generated by highway travel. To prepare for this, I used what has come to be called the “screw-and-glue” method of sheathing. This means that a bead of construc­tion adhesive was squeezed onto the entire length of every framing member before 3/8” plywood sheathing was screwed (not nailed) to its surface. This makes for a structure far more resilient to lateral wind loads than sheathing secured with nails alone.

before 3/8” plywood sheathing was screwed (not nailed) to its surface. This makes for a structure far more resistant to lateral wind loads than sheathing secured with nails alone.

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. Pollution-Induced Degradation of Bound Layers

Posted by on 16/ 11/ 15

Performance characteristics of bound pavement layers are known to be influenced by water-borne pollutants that cause changes in mechanical behaviour, ageing and degradation. With the exception of Portland cement concrete (PCC) pavements, this has not yet received much attention. Asphalt pavements are not seriously affected by inorganic pollutants, but most of the organic chemicals, including gasoline and motor oil, soften up or break down the asphalt binder leaving the asphaltic layer vulnerable to further degradation. Damage of the surface layer, due to ageing (stiff­ening because of ultraviolet light), traffic induced cracks and chemical degradation, opens an ingress route in the pavement system for pollutants from the surface.

In hot climates, salt can be moved by evaporating water to ...

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Coarse-Aggregate Skeleton

Posted by on 15/ 11/ 15

The first step, as in the U. S. method (see Section 7.2), is determining the volume of the skeleton of coarse particles and the voids between them available for the remain­ing SMA elements. Determining the volume occupied by the coarse aggregate skel­eton consists of defining its density and testing the coarse aggregate compaction (namely, the amount of air voids remaining among the coarse grains after compact­ing). As we know, the amount of air voids in a compacted coarse aggregate may be determined using the following methods:

• With dry aggregates, using the dry-rodded test after AASHTO T19 as in the U. S. method, or using a gyratory compactor, Marshall hammer, or on a vibrating plate

• Using a special lubricating agent[38] and chosen method of compaction

The substantial differen...

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