Some functional considerations in Loading Zone Design
By Rob Harley, HTG Architects – Tampa, FL
Authors note: Literally as this Blog was being formatted for posting, the news broke about the Amtrak derailment in Hoboken NJ. The historical event referenced in this post was in no way chosen due to the tragic accident in NJ, and HTG expresses our sincere sympathies and best wishes to the victims in Hoboken. Read more here.
The Granville to Paris “Montparnasse Express” was running about three minutes late. It was the 22nd of October in 1897 and the steam locomotive number 721 was trying to make up time in order to unload its 131 passengers on schedule. At 4:00pm, the train approached the station a little too fast, moving down the final stretch toward the intended stop at around 30 mph. As the train approached the station, the Conductor applied the Westinghouse made air-brake, which then summarily failed. Without sufficient braking resistance, the train slowly proceeded to bash through the safety buffers at the terminus and then continued on across the 100 foot long concourse of the station, its immense mass and momentum creating a slow motion battering ram. No people in the concourse were injured; presumably because they had time to jump out of the way of the slowly crunching locomotive, and could only turn to watch as the train punched its way through the opposite wall of the station. The wall was 2 feet thick. The ground on the other side of that wall was 33 feet down. The locomotive ended up in the position shown by the famous adjacent photograph. This particular photo was used on the cover of the book “An Introduction to Error Analysis” by John Taylor, and even on a 1991 album cover by a rock band called “Mr. Big”. I remember seeing a big black and white poster of the photo in the Engineering Department at the University of Colorado years ago with the unimaginative caption of “OOPS”. The event – for those geeky enough to look into it – has come to be called the “Montparnasse Derailment” and it is most remarkable for the lack of damage that was actually done in the mishap. Marie-Augustine Aguilard was the only person killed in the incident. She was unfortunately waiting for her husband on the plaza below. There were only 6 other minor injuries, and the 131 passengers walked away unscathed. Perhaps even more remarkable, was that when the locomotive was returned to the rail yard, it was found to have suffered little damage, and it was subsequently repaired and put back into service. The train Conductor was fined 50 Francs for driving too fast, and a distracted guard on the train was fined 25 Francs for failing to engage a back up hand brake. Marie’s surviving children were provided a pension by the railroad company. Needless to say, accidents today with far less drama than the Montparnasse Derailment, are considerably more expensive for all involved.
The loading and unloading of train passengers is not too much different than the loading and unloading of any valuable cargo. For Industrial buildings, and their loading and unloading requirements, we designers are still faced with similar factors. We too, have cargo, a moving vehicle, time pressures, usually a change in elevation, and a human component. The safety of that last item is of primary concern. There is a surprising amount of detail to cover in examining every aspect of loading zone design, and I won’t even try to do that in this post. So as usual, I will focus on the trends I see, and offer some tips based on personal experience.
I suppose you could broadly organize Loading Zone design concerns into three groups:
- Motion and Time
- Cargo Handling
Motion and Time:
For any loading situation on a building, it’s important to recognize the “intensity” of loading activities that will be expected. The loading requirements of a Distribution Center are more time and motion sensitive than the loading zone on an office building. The tighter the clearances, necessary turns, and dimensions available to an arriving truck, the longer it takes to position that truck to unload. For the occasional truck visit, no big deal – for a zone expected to handle multiple trucks every 15 minutes or so, it’s a really big deal. So what are the trends? “Low use” loading zones for commercial buildings haven’t changed much in the last twenty years. Truck wells are still acceptable, and access can be highly variable and site dependent. The trending changes are centered almost entirely on Distribution facilities. Rapid “fulfillment”, and “just in time” delivery, are driving bigger dimensional requirements for truck loading areas. The standard 120 feet for a single truck court depth is often pushed to 130, or even 150 feet for many new distribution centers. Planning truck traffic to enter a loading zone so that drivers can look over their left shoulder when backing in is still important for high speed loading and unloading. Overlaying of truck turning radius “templates” on the site plan during design is also still essential. Loading door spacing is also increasing. Although 12 feet on center has long been the minimum standard, for new distribution functions, it is generally regarded as too tight for rapid truck approaches and departures. Even the formerly generous 13’-4” center to center dimension for loading doors is getting stretched as both bay sizes and traffic intensity increase.
It is more and more common now, even for speculative warehouse buildings, to design a deeper “staging bay” into the rear structural bay of the building. 50 to even 60 feet is a common dimension. This allows for safer and more efficient staging and loading of arriving or departing product. Flexibility in loading dock heights also continues to be an increasingly requested option. A number of build to suit buildings I have been involved with have planned “van high” loading areas to accommodate frequent van visits for example. Another trend with respect to loading height flexibility I have seen recently is the use of pre-fabricated, concrete drive in ramps. Low maintenance and sturdy, these ramps allow a property owner to configure ramp access to a new tenant without the process of building, and/or demolishing, cast in place concrete ramps. The companies that manufacture and install them, also have services for relocating them, thus simplifying the meeting of new tenant requirements in a spec building. Another trending development influencing industrial buildings is the increasing use of “intermodal” delivery trucks. These trucks carry containers offloaded directly from ships or trains, and the deck height of those trucks is in the range of 53”-56″, not the traditional 48” dock height. “Freight forwarding” facilities have long been built to these higher truck deck heights, but I have not yet seen speculative buildings, at least in the local market, making attempts to address this dimensional issue by raising the dock height . With all the changes being driven by e-commerce and inland ports though, I would not be surprised to start seeing even generic spec buildings begin to accommodate these requirements, at least in certain areas.
Loading areas are inherently accident prone places. This is true for several reasons, not the least of which is that in a reasonable recognition of common sense; Building Codes allow the omission of safeguards around loading areas due to their obstruction of loading activities. But that means a nasty fall is always possible, and this is particularly acute for indoor dock high loading slots. Indoor loading slots are usually built to accommodate high value cargo that needs to be locked inside a building while still in the trailer. I once had a facilities manager for an Office Supply distributor I was doing a building for politely explain to me that a trailer full of printer ink cartridges could easily top $1,000,000 in value. I understood his point. These indoor loading conditions create a special hazard though, and safeguards should be carefully considered and arranged. Sometimes guardrails on the sides of these slots are designed to be removable for offloading from the side. But regardless of the codes exception, the sides of these loading areas should be fitted with guardrails, leaving only the back wall unguarded. Safety gates for open, unoccupied standard loading doors are a good idea too, and are often installed by tenants in spec buildings they lease.
Accidents are not limited to falls however. A moving forklift for example, can do considerable damage to anything it strikes. A number of years back, I recall standing awestruck with a property manager in a just completed warehouse I had done, staring at a 10 inch square steel column with 3/8” thick walls that was nearly sliced completely through about 30 inches off the floor. A forklift driver had misjudged his clearance, and the forks of the rapidly moving lift caught the corner of the square column, slicing right through it. The area around the column was cordoned off since it had buckled, and the repair was, needless to say, “involved”. For this reason, I usually recommend that clients consider using round pipe columns for warehouse roof support. They are less likely to be cut in such a way than the more popular square columns. The circular surface of pipe columns provides a glancing angle of attack to swinging forklift forks, rather than a more vulnerable 90 degree corner. I have to admit though, that my recommendations for this approach have not resulted in any developing trend. The industry still sees round pipe columns as an “old school” relic, and the square steel tube columns continue to be the default choice. Another, more frequent spot for forklift impact is the overhead door tracks to either side of a loading door. The trend I see these days, and one I endorse, is the rejection of the traditional pipe bollard protection at these locations, in favor of wall mounted “zee guards”. Composed of 3/8” thick steel plate bent into a “zee” shape, these guards are bolted to the wall over the door tracks up to about 4 or 5 feet above the floor. Not only do they take up less space than traditional bollards, but they are easier to replace when hit. When a bollard needs replacing due to an impact, a property manager is faced with a big task. It involves cutting the floor, excavating 4 feet down below the slab, re-compacting the subgrade….. you get the picture, it’s not pretty.
As I re-visited the topic outline I put together for this blog effort, I was a bit discouraged at all the items I wasn’t able to address in this brief posting. There is truly a lot to talk about that I didn’t get to, from all the safety equipment available, to even aesthetic minded tricks one can employ in order to help keep loading areas looking clean and functional. Perhaps there’s a follow up in the future. In any case, I’m just glad that the loading platforms I deal with on a regular basis aren’t 33 feet above the ground.
Next Post: “Insane in the Membrane” – Trends and issues for large Commercial roofs.