Van and Lawrence Smith founded Smith Bros. Concrete Contractors, Walden, N.Y., in 1975. They bought a truck for $300 and had to borrow $3 for gas to drive it home. For the first several years they installed block and brick masonry but gradually shifted their emphasis to poured foundations for residential homes. Van says that 5 years ago there was one computer in their office, and staff took turns using it. But he sensed the increasing importance of office computers and later placed a computer on every desk.
Three years ago, at the World of Concrete, they visited with companies selling “total stations”—survey instruments capable of faster, more accurate layout work. To Van they were extensions of computer technology, and he decided to invest. He recalls the sales person urging them to spend a little more money for an instrument capable of linking up with a “data collector.” So they bought a Trimble construction total station (requiring two men for layout) and later added the data collector, an LM-80 Layout Manager— a very contractor-friendly unit. This enabled them to use the full potential of total stations for layout work. More recently the company purchased a “robotic total station” with a touchscreen data collector, the instrument they prefer to use now. The younger generation, Van's 23-year-old son, Conor; now does most of their layout work.
One of the unexpected results of total station technology was that the Smith brothers were able to position their business in more non-competitive areas of work. From installing 160 foundations they downsized to 80 custom foundations per year. Their competition currently refers many projects to them because of the intricate layout work and complicated forming needed. This year they received the “Foundation from Hell” award given by the Concrete Foundation Association (CFA). “When we set up the 60 layout points for the foundation in the data collector, we discovered a 4-inch error on the architectural drawings,” said Van. “We saved several thousand dollars by finding the error long before the walls were constructed.”
Types of equipment and how they work
Lawrence Smith, segment manager for the construction instruments division for Trimble, Dayton, Ohio, says, “Total stations combine theodolite technology (which accurately measures angles on both the vertical and horizontal axis) with electronic distance meters (EDM).” Before going to a site, you determine the layout points for a project relative to at least two known control points on the property survey. Once onsite, two people lay out each of the points. Though plans are two-dimensional on a horizontal plane, a total station will accurately locate the points, even when the land is sloped or uneven.
Elements of a total station
The instrument. There are manual total stations and robotic total stations. Each one uses laser and infrared technology. Manual stations require two people to shoot points, and the data collector is located at the instrument. Only one person is needed for layout work with a robotic instrument because it automatically follows the target everywhere. The data collector is located at the target and communicates with the instrument by radio.
Data collectors. They are small, powerful computers with software for locating and recording the layout points and control points. Data collectors can be separate units or built into a total station. Van and Conor use a Trimble LM80 with their manual station and a TDS touchscreen unit for their robotic station. You can use them to plot layout points, or you can download computer assisted drawings (CAD) directly into them. If you manually locate points, software guides you through the process. Van added a layout software package called “Survey Pro” to the TDS collector for his robotic station.
Once points are plotted, the information is stored in a job file on the data collector for future use. Hundreds of project folders can be stored for use whenever they are needed.
The target. It is very different from the traditional “sticks” or “rods” used with older surveying instruments. Located at the top of a target is a 360° series of prisms that reflect light back to the total station. From this, distance and direction are determined. For robotic instruments, a radio and either a data collector or a keyboard are mounted on the target.
Holding a target plumb is a very important worker skill when locating a layout point. This is the reason for many layout errors. For control, “Bi-Pods” are available—two adjustable legs that secure the target like a tripod. This way the target can be kept plumb while locating a layout point.
Checking for “closure”
Total stations can accurately locate layout points within 1/16 inch of their ideal location. Van says their goal is to be within ? of an inch for their foundation work. But to do this requires skill, understanding, and a commitment to checking the work. The process starts by checking layouts for “closure,” which refers to closing boundaries or ending on the same point from which you started when laying out buildings and foundations. When you plot the corner points around a structure, you should end at the starting point. If there is a separation between these two points, the error must be resolved. If you input points from a plan, either there is an error on the plan or there is a calculation error on your part. If you download plans directly, the error is a drafting error.