OVERVIEW OF EARTHQUAKE RISK CIVIL ENGINEERING CONTEXT BASIC INFORMATION AND TUTORIALS

The first step in understanding earthquake risk is to dissect the earthquake risk or loss process into its constituent steps. Earthquake risk begins with the occurrence of the earthquake, which results in a number of earthquake hazards.

The most fundamental of these hazards is faulting, that is, the surface expression of the differential movement of blocks of the Earth’s crust. Faulting can be a simple “mole-track” lateral movement, or a major vertical scarp, or may not even be visible.

In most cases, faulting is typically a long narrow feature, and therefore affects a relatively small fraction of the total affected structures and persons. Affecting a much greater number of structures and persons is shaking, which is typically the primary hazard due to earthquakes.

Depending on the earthquake, liquefaction, other forms of ground failure, tsunamis, or other types of hazards may be significant agents of damage. For various reasons, many buildings, portions of the infrastructure, and other structures cannot fully resist these hazards, and sustain some degree of damage.

Primary damage can vary from minor cracking to total collapse. Some building types are more vulnerable than others, but even when a building sustains no structural damage, the contents of the building may be severely damaged.

For certain occupancies, such as hospitals or emergency services dispatch centers, this damage to contents (laboratories, specialized machinery, communication equipment, etc.) can be very important. Additionally, these various kinds of primary damage can lead to other secondary forms of hazard and damage, such as releases of hazardous materials, major fires, or flooding.

Damage results in loss.

Primary loss can take many forms — life loss or injury is the primary concern, but financial loss and loss of function are also of major concern. The likelihood of sustaining a loss is termed risk . Primary losses lead to secondary forms of loss, such as loss of revenues resulting from business interruption and loss of market share and/or reputation.

QUANTITY ESTIMATING CIVIL ENGINEERING PROJECTS BASIC INFORMATION AND TUTORIALS

In Canada, parts of Europe, and on most road construction projects in the United States, the estimated quantities of materials required on the project are determined by a professional quantity surveyor or engineer and provided to the interested bidders on the project.

This is often referred to as a unit price bid. In this method of bidding, the contractors are all bidding based on the same quantities, and the estimator spends time developing the unit prices. For example, the bid may be $47.32 per cubic yard (cy) of concrete.

Because all of the contractors are bidding on the same quantities, they will work on keeping the cost of purchasing and installing the materials as low as possible.

As the project is built, the actual number of units required is checked against the original number of units on which the estimates were made. For example, the original quantity survey called for 715 linear feet (lf) of concrete curbing.

If 722 lf were actually installed, then the contractor would be paid for the additional 7 lf. If 706 lf were used, then the owner would pay only for the 706 lf installed and not the 715 lf in the original quantity survey.

This type of adjustment is quite common. When errors do occur and there is a large difference between the original quantity survey and the actual number of units, an adjustment to the unit price is made. Small adjustments are usually made at the same unit rate as the contractor bid.

Large errors may require that the unit price be renegotiated. If the contractor is aware of potential discrepancies between the estimated quantities and those that will be required, the contractor may price his or her bid to take advantage of this situation.

With a belief that the estimated quantities are low, the contractor may reduce his or her unit price to be the low bidder. If the assumption is true, the contractor has the potential to make the same profit by distributing the project overhead over a greater number of units.