Blog Archives

Models for Subgrade Soils and Unbound Granular Materials

Posted by on 20/ 11/ 15

The purpose of this section is to introduce some of the constitutive models devoted to routine, as well as advanced, pavement analysis and design. For all these models, moisture or water pressure are not taken into account. They are written, here, in terms of total stresses – i. e. the effects of pore water pressure and/or pore suction are subsumed into the mechanical response of the materials and are not explicitly described.

Nowadays, models for subgrade in pavement engineering have been split in two categories dealing with the main mechanical behaviour which needs to be taken into account:

• resilient behaviour (see Fig. 9.3); and

• long term elasto-plastic behaviour.

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Generation of Vectors of Multivariate Random Variables

Posted by on 20/ 11/ 15

In preceding sections, discussions focused on generating univariate random variates. It is not uncommon for hydrosystems engineering problems to involve multiple random variables that are correlated and statistically dependent. For example, many data show that the peak discharge and volume of a runoff hy­drograph are positively correlated. To simulate systems involving correlated random variables, generated random variates must preserve the probabilis­tic characteristics of the variables and the correlation structure among them. Although multivariate random number generation is an extension of the uni­variate case, mathematical difficulty and complexity associated with multi­variate problems increase rapidly as the dimension of the problem gets larger.

Compared with generating univaria...

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Sign Assemblies

Posted by on 20/ 11/ 15

The sign panel, the support, and the embedment or anchorage system are the three components of a sign assembly. Each component contributes to the effectiveness, structural adequacy, and safety upon impact of the device. The sign assembly must be structurally adequate to withstand its own weight and the wind and ice loads subjected to the sign panel. In some northern climates, this requirement includes the forces created by snow ejected by snowblowers or the lateral forces resulting from snowplow activity. The majority of the design guides for each state contain recommendations on the size, number, and type of support required in different regions of the state. These guidelines are based on the size of the sign panel and the recurrent wind intensity...

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SIDEWALKS AND WALKWAYS

Posted by on 20/ 11/ 15

Many local zoning ordinances and construction standards specify that sidewalks be built on both sides of residential streets. These requirements were developed during an era of lower land values and lower construction costs, and should be reviewed in the context of today’s higher costs.

Following are guidelines for sidewalks and walkways:

• Construct sidewalks on one side rather than both sides of local streets, and consider elimination altogether on lightly traveled streets.

• Eliminate sidewalks around deadend streets and cul-de-sacs.

• Minimize placing homes facing collector and higher-order streets, thereby reducing or eliminating the need for sidewalks on these streets.

• Replace infrequently used sidewalks on streets with pathways between _ groups of residences, bus stops, st...

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Orient the House to the Sun

Posted by on 20/ 11/ 15

Подпись:Подпись: GNOrient the House to the SunPlacing the long side of a house along the east – west axis exposes the south elevation to year – round light and warmth. In summer, this orientation minimizes overheating on the short east and west elevations. Grouping private and unoccupied spaces on the north side of the house, where they act as insulators for the south-facing public Bedroom rooms, maximizes the benefit of southern exposure.

North

Finding True North

Подпись:Подпись:At the bottom margin of U. S. Geologi­cal Survey maps, there are three north bearings: magnetic north, true north, and grid north Magnetic north is compass-needle north, but it’s not helpful for solar siting, which calls for true north, indicated by the star. The difference between these bearings is the declination, in this case,

13.5 degrees.

from the rest of the house)...

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General Objectives, Strength and Deformation

Posted by on 20/ 11/ 15

With the use of numerical modelling, engineers aim to obtain the displacement fields as well as the stress values (effective stress, pore pressure and suction) in the road and earthworks sub-structure. The numerical modelling allows the understanding of the behaviour of the geostructure and the analysis of an optimal design. In order to be successful, the computational tool should, then, include the main physical processes of the rheology of the materials that make up the structure.

The behaviour of granular media is mainly dependant on an inter-granular fric­tion as well as on the applied stress which modifies the rigidity and the strength of the material. It is highly non-linear and irreversible. Figure 9.2 summarizes the main stress-strain aspects.

Fig. 9...

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Techniques TURNING CORNERS IS TRICKY WORK

Posted by on 20/ 11/ 15

COMBINING AN ENCLOSED SOFFIT with a gable – end roof overhang means that you need to construct a boxed return. The return creates the nailing sur­faces required to bring the soffit and fascia trim around the corner of the house. Here’s how to do the job:

1. Use 2x lumber to make the framing for the boxed return, which consists of a triangular piece cut to match the roofs pitch and a straight board that ver­tically extends to the gable wall.

2. Fasten this assembly to the bottom edge of the barge rafter and the back wall. The soffit paneling must be attached prior to the aluminum cladding.

Techniques TURNING CORNERS IS TRICKY WORK

3. Run electric cable through the corner soffit for an outdoor light...

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Need Determination and Placement of Traffic Signs

Posted by on 20/ 11/ 15

Estimates on the number of signs present on our roadways vary drastically. An NCHRP synthesis indicated 58 million signs, while a study for the FHWA estimated that there are approximately 250 million sign assemblies on the U. S. roadway system [15, 16]. Signs contribute an important role in increasing the safety of the roadway by providing regulatory, warning, control, and guidance information to the driver. Every sign that is installed on its own support system, however, provides a fixed object for a potential collision. Even a relatively small sign on an apparent weak support can have severe consequences when struck at high speed.

TABLE 7.1 Design Dynamic Deflections of Various Barrier Types

Barrier type

Design

deflection,* ft

Design

deflection,* mm

Concrete safety shape
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STEP 4 FRAME THE STAIRS

Posted by on 20/ 11/ 15

I taught night school at a community college for 20 or so years. My students were apprentice carpenters learning how to build houses. Often, students were hesitant to take on the task of building stairs because of the presumed diffi­culty. It came as a surprise to most of them that building stairs—especially a simple, straight flight of stairs—is actually quite easy. If you can do some basic math and know how to use

Because we are using 11/2-in.­thick treads, 11/2 in. has to be cut from only the first riser to make each rise equal after thetreads are screwed in place.

a framing square and a circular saw, you can build stairs...

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Origin of Mechanical Properties in Pavement Materials

Posted by on 20/ 11/ 15

The materials that comprise the lower parts of the road and which form the subgrade are all geomaterials – particulate solids with pore spaces occupied by a combina­tion of water and air in varying proportions. The solid particles are, for the most part, crystalline. They are derived, ultimately, from geological sources. Individually the grains have considerable strength which means that the mechanical response (strength, stiffness, resistance to development of rutting) of an assembly of parti­cles is a primarily a consequence of the way the individual grains interact with one another and not of their own properties.

The primary contribution to mechanical property derives from the ease or diffi­culty with which one particle can be moved adjacent to another particle...

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