Uppeak probably exists for 5 minutes and down peak for 10 minutes, and two and four way traffic, if they occur at all, can be considered to be severe cases of unbalanced interfloor traffic. Interfloor traffic is caused by the normal circulation of people around a building during the course of their business. Sometimes this traffic is called balanced two way traffic as it involves both up and down trips, and it is balanced because passengers usually return to their original floor after moving about the building.
Figure 4.9 Spatial movements of lift cars during balanced interfloor traffic
Figure 4.9 is taken from a computer simulation of an hour of office activity. Note that the figure can be reversed or inverted and still no discernable pattern can be seen in the spatial activity of the lifts
4.4.5 Other traffic situations
Figure 4.10 Another arrival profile for morning uppeak with two starting times
Page 93
It is possible to find office buildings where no dominant traffic flows occur, especially where FLEXITIME working is used. Sometimes the uppeak situation occurs twice, as in Figure 4.10, but at a lower
intensity. And obviously traffic patterns are different in institutional and residential buildings; but often dominant patterns similar to those defined above do emerge and hence ease design procedures. The effect on a lift system of applying a non-smoking regime in a building, where smoking is not permitted inside the building and smokers have to go outside, can have a significant effect. Even today 24% of the people smoke and might crave one smoke per hour.
4.4.6 Summary of traffic conditions
Traffic conditions may be summarised as follows:
■ the duration of the uppeak traffic condition is about 5 minutes ■ the duration of the down peak condition is about 10 minutes
■ the two-way traffic condition may exist for one to two hours dependent on the arrangements for the midday break
■ the interfloor traffic condition exists for most of the working day and therefore is very important. The distinctive “fingerprints” of uppeak, down peak and balanced interfloor traffic patterns, as represented by the spatial movements of lifts, are:
Uppeak: The lifts arrive at the main terminal, load with passengers, and move up the building stopping often until the last stop when they express return to the main terminal. During the peak 5-minutes there is a “staircase” pattern.
Down
peak: The lifts stop at a few floors in the building, loading with passengers andthen express to the main terminal. After unloading the passengers the lifts make an express run back up the building. There is a small
“staircase” pattern in the reverse direction to the uppeak case.
Interfloor:There is no discernable pattern for a balanced interfloor traffic condition. 4.5 TRAFFIC DESIGN
4.5.1 Introduction
Why is there a need for traffic design? This could be answered as follows:
■ To size a lift installation to serve a traffic requirement or meet a capital/recurrent financial requirement.
■ To compare competitive tenders.
< previous page
page_94
next page >
Page 94
It is extremely difficult to compare competitive tenders where no standardised methods of specification or common design procedures are used. Each manufacturer and lift consultant often use different methods, and are not keen to explain their approach. Many methods that are published are often sketchy and some are inaccurate. In addition, the use today of modern control systems radically alters some of the design assumptions. An easy to use, acceptable and standard design method will be
presented here. This should enable a prospective designer to gain a better understanding of the design procedure and be able to use it better.
Little theoretical or analytical work was carried out into traffic design and control, until recently.
Simulation techniques were used by earlier workers (Browne and Kelly, 1968), who considered their use essential to investigate better design methods and to develop new traffic supervisory control techniques. Simulation is a tool generally used only when a sufficient mathematical definition does not exist.
By the 1970s, a recognised method of calculation had evolved, for the uppeak traffic sizing, based on the mathematical determination of average highest reversal floor (H) by Schroeder (1955), average number of stops (S) by Basset Jones (1923) and average number of passengers (P). The next lesson looks at statistical modelling theory, which provide a sound mathematical base.
The formulae by Barney and Dos Santos (1977) for the calculation of the passenger handling
performance of lift systems are now universally accepted. Lift makers often use tables specific to their product range to estimate round trip times, interval, handling capacity, etc.
The problem in sizing lift systems is to match the demands for transportation from the building’s
occupants with the handling capacity of the installed lift system. This procedure should also result in an economic solution. The conventional procedure used in the traffic design of lift systems is to determine the handling capacity for the uppeak traffic situation. This approach is sensible as the uppeak traffic condition does yield to analytic techniques, although some of the assumptions making this possible are difficult to justify in the real life situation.
4.5.2 Some Definitions
What is uppeak or incoming traffic? This has been defined in Section 4.4.1 as Definition 4.1. The idealised profile of Figure 4.4 extends Definition 4.1 to allow a 5 minute uppeak passenger arrival rate to be defined.
Definition 4.6:The uppeak percentage arrival rate (%POP) is the number of passengers who arrive, at