Utilities. These are programs that arrange information or do arithmetic; for example, spreadsheets and report generators databases. Most estimating programs fall into the utilities category. Databases. These contain raw information, for example, prices of plumbing fixtures, that the estimator must analyze and choose from. Expert Systems. These are programs that question the estimator, then use the answers to produce an estimate. (Expert systems are sometimes referred to as artificial intelligence systems.) Some commercial packages may contain two or more of these. Computer aided estimating has now specialized with software blurring these distinctions. This goes across the construction industry where you see competitors using the same software with certain information customized. One sees a single brand of software in use by contractors and another by designers and yet another by home builders. Contractors tend to use utilities that talk to their expert system for material control and fabrication. Designers use specialized expert systems for the specific work they performed (i.e., environmental remediation), and the home builder may have sales people using an expert system that was created in a utility with pricing from window and door vendors.

After client approval of the construction documents and selection of a construction bidding method, the architect may assist in the selection of contractors to bid the work; preparation of bid forms; issuance of bidding documents for competitive bidding; answering inquiries from bidders; and preparing and issuing any necessary addenda to the bidding documents. Furthermore, the architect may assist in analyzing bid proposals and making recommendations to the client as to the award of the construction contract. The architect can also assist in preparation of the construction contract. Bidders may elect to change their bid on the basis of certain conditions, such as errors in the bid, changes in product cost, changes in labor rates, or nonavailability of labor because of other work or strikes. Each bidder is responsible for providing for any eventuality during the period the bid is open for acceptance. Unless provided for otherwise, bidders may withdraw their bid before acceptance by the client, unless the client consents to a later withdrawal. If all conditions of the instructions to bidders have been met, then after the bids have been opened, the bids should be evaluated. The low bid especially should be analyzed to ensure that it reflects accurately the cost of the work required by the contract documents. The bids may be compared with the architects construction cost estimate that was prepared on completion of the contract documents. The client can accept a bid and award the contract to the selected bidder, who then becomes the contractor for the

1/4-in plate glass 26 3/4-in plywood 28 1/2-in gypsum board, both sides of 2
4 studs 33 1/4-in steel plate 36 6-in concrete block wall 42 8-in reinforced-concrete wall 51 12-in concrete block wall 53 Cavity wall, 6-in concrete block, 2-in air space, 6-in concrete block 56 frequencies above the coincidence frequency, the curve tends to recover its preceding slope. There are few practical limp materials useful for ordinary building panels. Soft sheet lead is occasionally used for specialized barriers, as described in Art. 11.80, or is applied to other panel material to increase the mass of the composite without increasing its stiffness. In addition, damping materials (Art. 11.79.4) can be applied to the panels to damp out their vibrations quickly and to increase the energy loss as the panels vibrate. Figure 11.93 shows another characteristic of barriers that further complicates their performance. While single, solid panels have somewhat smaller transmission losses than the mass law predicts, a double wall, a barrier comprising separated wythes or leaves, of the same total weight produces greater transmission losses than the mass law predicts. If the mass of a single, solid panel is divided into two separate, unconnected layers, the only energy transfer between them occurs via the air between the layers. Air is not stiff; it can sustain little of the shear wave, and it is not an efficient transmitter of the back-and-forth motion of one layer to the other (except at certain resonant frequencies). As a result, particularly in the midfrequencies, the sound transmission loss actually exceeds the mass-law values, often considerably. The greater the distance between layers, the better the performance. Theoretically, the sound transmission loss should increase about 6 dB for each doubling of the width of the airspace. In practice, however, the increase in decibels is somewhat less than