Tag Archives: Safety

Impactable Dock Doors Help Increase Safety in Warehouses

All photos courtesy TKO Doors

All photos courtesy TKO Doors

by Josh Brown

Safety statistics are a dramatic way to get people’s attention to help them understand the connection between a facility’s safety efforts, loading dock equipment (in this case, the doors), and return on investment (ROI) when specifying equipment for a project.

Recent studies by the U.S. Bureau of Labor Statistics (BLS) such as, OS NR 11/07/2013 News Release: Workplace Injuries and Illnesses–2012, noted there are almost three million work-related injuries and illnesses recorded annually. Of those, a large percentage of all recordable injuries result from slip-and-fall hazard injuries that can cost companies several billions of dollars per year.1

An example of the easiest way to avoid slips and falls in a warehouse facility is by trying to eliminate and control the hazards. Many of these can be avoided by specifying the proper loading dock doors.

Workplace injuries
The 2007 Liberty Mutual Workplace Safety Index indicates falls were the second leading cause of all workplace injuries—with 13.6 percent of direct costs associated with such injuries adding up to a staggering $6 billion. Additionally, the National Safety Council (NSC) estimates workers’ compensation and medical costs associated with employee slip-and-fall accidents are approximately $70 billion annually, and there is little relief in sight.

When specified correctly, wind-load doors offer the combined benefits of superior protection inside and outside a facility.

When specified correctly, wind-load doors offer the combined benefits of superior protection inside and outside a facility.

Loss of productivity is often a side effect of worker injury. On average, workers who are injured as a result of a slip-and-fall accident spend more days away from work than those hurt by other causes.

When considering workplace falls, most people immediately think of falls from a height, yet, the BLS suggests the vast majority (i.e. 65 percent) occur as a result of falls from same-level surfaces. Moreover, there are industries of particular interest when it comes to determining the allocation percentages for these injuries. These include warehouse, wholesale/retail, and manufacturing industries that together accounted for the greatest proportion of injuries resulting from same-level falls—more than 60 percent.

Safety standards
Safety in warehouses and manufacturing facilities is regulated by a series of standards developed by the Occupational Safety and Health Administration (OSHA). The main focus is to prevent work-related injuries and illnesses through continuous monitoring and inspections of facilities and modifications to these standards.

Loading dock locations are an important area to consider when specifying safe materials in a warehouse. There can be up to hundreds of doorways along the typical loading dock; these openings can permit moisture to enter the area to mix with dirt, debris, and oil, creating a dangerously slick surface.

Many companies are realizing warehouse safety begins with planning and prevention on the dock and inside the warehouse during the design, construction, or retrofitting of a facility. With this in mind, there is no better place to start than with the warehouse doors separating the inside of the facility and employees, from a host of potential hazards.

Dock doors can be damaged by forklift traffic and products on tight, busy docks as workers try to maneuver materials into and out of trailers. Impactable dock doors can prevent gaps from forming between the door panels when they are hit, and reduce the amount of elements and moisture that can enter a facility.

As storms or high-wind events approach, warehouse employees can quickly and easily slide the slide locks and pins into place for added protection.

As storms or high-wind events approach, warehouse employees can quickly and easily slide the slide locks and pins into place for added protection.

Wet floor surfaces
A particular area of concern regarding slip-and-fall injuries are wet floor surfaces. Under OSHA 29 CFR 1910.22(a)(2), Walking-Working Surfaces, the floor of every workroom should be maintained in a clean and, so far as possible, dry condition. Where wet processes are used, drainage shall be maintained, and false floors, platforms, mats, or other dry standing places should be provided where practicable.

Impactable design dock doors allow them to stand up to the abuse experienced on the dock. When a forklift or other object collides with the door, the impact causes the plungers to retract, allowing the door to release from the opening, thus preventing panel damage. After the door is knocked out from the track, a light pull on the door handles resets the door, putting it back in operation quickly without damage. This keeps the floors dry and safe, and ensures clients remain in compliance.

Since door and track damage are some of the leading causes of broken seals and gaps on doors that can cause moisture to build up on the warehouse floor, many impactable models also feature an impactable track. These tracks can run the entire length of the door opening to protect against potential damage from impacts from forklifts, masts, and materials without sustaining any damage or exposing the facility to gaps that can let in rain, snow, condensation, or ice that can spell disaster for both pedestrian and forklift traffic.

Additional injuries
Slips and falls are not the only types of injuries that loading dock doors need to contend with. The National Weather Service (NWS) provides data showing both hurricanes and tornados are the second- and third-most fatal weather hazards in the United States over the past decade—up from the previous 30-year average.

Over the past few years, hurricanes have made headlines and caused billions of dollars in damage to structures and products, and injuries to people, along the Gulf Coast and Eastern Seaboard. All the country’s coastlines and low-lying inland areas are susceptible to high-wind events associated with these storms and the potential devastation they cause when wind speeds can range from 144 to 241 km/h (90 to 150 mph). Even if an area has been spared from dealing with these disasters in the past, building owners should be prepared for whatever nature blows their way.

Of particular concern are commercial operations, especially warehouses and distribution facilities that find themselves increasingly exposed to danger and injuries as a result of numerous overhead doors and 24-hour operation. The potential for billions of dollars in damage and injuries to personnel when a hurricane makes landfall, or a tornado touches down, is motivation enough to storm-proof operations during construction.

Protection from high-wind events does not mean sacrificing function, these doors provide operation year-round.

Protection from high-wind events does not mean sacrificing function, these doors provide operation year-round.

Having a door that can withstand high winds is crucial to a building’s survival and employee safety. About half of the damage to a distribution center’s contents, and injuries sustained by employees during these events, is a result of the dock doors being ripped from their tracks and off the walls.

Moreover, the door is the only moving part one must consider on the building’s structure. Most other components—such as the walls or roof—are securely fastened into the building materials. In the parts of the country that will experience these devastating storms and tornados, commercial buildings must have doors that stand up to the pounding wind and flying debris, yet do what they are supposed to routinely do, which is open and close to efficiently handle truck traffic on the loading dock.

Whenever commercial building owners are unaware of the importance of proactively designing and building to reduce damage to their facilities and the disruption to their schedules, the insurance companies and, consequently, the code-writers for state and local governments, will remind them.

Traditionally, the South has been the busiest and hardest hit by hurricanes and tornados. However, as of late, the Northeastern Seaboard has also fallen victim to some of Mother Nature’s most devastating storms. In the wake of 2012’s Hurricane Sandy, facilities from Canada to North Carolina to Wisconsin have seen the effects these storms can have.

Storm damage
Do super-storms, high-wind events, and the potential devastation provide companies with an option to help reduce losses from facility damage and business interruptions? How can warehouses and other facilities protect assets from these storms?

In 2013, the American Society of Civil Engineers (ASCE) released a new edition of Wind Loads, a guide focused on ASCE/Structural Engineering Institute (SEI) 7-10, Minimum Design Loads for Buildings and Other Structures. This revised text includes information dedicated to wind load provisions for both residential and commercial buildings. Aimed at an audience of architects, engineers, and specifiers, it includes simplified calculation methods and guidelines to help these professionals provide clients with the most accurate recommendations to protect buildings.

The result of Hurricane Andrew’s impact in 1992, that caused $26.5 billion dollars and killed 65 people, was an updated ASCE Wind Loads guide. The storm also led Florida to enact the country’s toughest state building codes to ensure structures are tougher than the storms. These regulations encompass 24 product categories—including overhead sectional doors.

This photo provides details of the slide locks and pins that offer enhanced security during high-wind events.

This photo provides details of the slide locks and pins that offer enhanced security during high-wind events.

Florida requires buildings and their components, including doors, withstand wind pressures generated by winds ranging from 177 to 241 kph (110 to 150 mph). Additionally, the doors must stand up to a level of ultraviolet (UV) rays from the sun that could compromise the strength of the panels. It is no wonder Miami-Dade County is leading the building standards charge against Mother Nature in light of the devastation left from Andrew.

Notice of approval
Within the world of building codes, ‘wind load’ refers to the pressures exerted on a structure and the components comprising the structure due to wind. Wind pressures are assumed to act both toward (i.e. positive pressure) and away (i.e. negative pressure) from a building’s surface.

Stepping into this role as a building protector are wind-load-rated, impactable loading dock doors, already designed to stand up to impacts on the inside of the building. Now, these doors are available in wind-load-rated designs to even meet the Miami-Dade requirements for resistance to forces and impacts outside the building.2

Impactable dock doors were introduced to address the common damage and downtime issues associated with traditional metal overhead doors used in distribution centers and warehouses. Traditionally, these openings are similar to a standard garage door, and hardly built to take a hit from a forklift much less withstand hurricane force winds.

The widely accepted use of impactable dock doors has enabled distribution centers, manufacturing plants, and other commercial facilities to address the common damage and downtime issues that come with forklift impacts, saving considerable damage, energy loss, and reducing operating costs.

With an impactable door protecting against forklift impacts inside the facility, a logical next step was to enable them to stand up to high-wind events and flying debris from hurricanes, tropical storms, or tornados that can injure employees on the docks and in other areas of a facility.

The features of these wind-load doors are similar to those on standard impactable doors mentioned earlier that can help prevent moisture infiltration and subsequently slips and falls, with an extra layer of protection. They include heavy-duty, retractable plungers, an impactable track, damage-resistant panels with polycarbonate skin, and slide locks with lock-out pins.

If a forklift or flying debris collides into an impactable dock door, the heavy-duty retractable plungers release the panel from the door guide, absorbing the impact and preventing damage or injuries. The damage-resistant panels with polycarbonate skin also guard against damage from flying debris and materials, as well as provide a layer of UV protection from the sun’s harmful rays that can weaken the doors panels.

The high-density impactable tracks mounted flush to the jambs are another part of these unique wind-load-rated impactable assemblies, which enable the door to remain attached to the wall. Unlike standard door tracks, the high-density tracks fight off the most abusive forklift impacts on the inside, while providing the necessary strength to withstand negative and positive wind pressures on the outside during a storm.

Impactable doors with wind load still protect against forklift impacts.

Impactable doors with wind load still protect against forklift impacts.

In regard to wind storms, negative wind pressures are a particular issue with overhead doors in general. To combat these forces, wind-load-rated impactable doors have multiple slide-locks mounted securely to a steel plate on the panels. As a storm approaches, the crew can engage the slide locks into holes along the height of the guide track and secure with a pin attached to the tracks. This is an extremely important consideration in facilities that have a large number of these doors with limited time and resources to prepare for a high-wind event.

As a way to combat these

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high-wind events in accordance with the Florida Building Code (FBC), rigorous testing establishes if a door design meets static air pressure resistance required by American National Standards Institute/Door and Access Systems Manufactures Association (ANSI/DASMA) 108, Standard Method for Testing Sectional Garage Doors and Rolling Doors: Determination of Structural Performance Under Uniform Static Air Pressure Difference, or ASTM E330, Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights, and Curtain Walls by Uniform Static Air Pressure Difference, specifications. Though static air pressure (positive and negative) is one issue (measured in lb/sf), some localities are requiring door testing to determine the ability to resist penetration of airborne debris. The testing involves hundreds of simulated wind gusts and impacts from a 2×4 stud shot from a cannon at 15.24 m/second (50 ft/second).

Essentially, these impactable door designs meet FBC as determined by the testing. The same door panels, which stand up to the forceful impact of speeding forklifts carrying heavy loads, were able to pass the wind gust and projectile tests and still provide coverage for the doorway. To provide additional assurance to overcome these forces, there is a flexible tubular frame reinforced with a steel angle inside the panels.

Conclusion
While facilities in the Gulf region and other areas along the Atlantic Coast have suffered billions of dollars of damage and injury due to high winds, innovative and stringently tested wind-load-rated impactable doors can help distribution and warehouses facilities of all sizes obtain reduced property damage and maintain a more secure loading dock after the storm, leading to minimal disruption to the supply chain and help reduce slip and fall injuries.

Notes
1 For more information, visit www.bls.gov/news.release/archives/osh_11072013.htm. (back to top)
2 Visit www.miamidade.gov/building/pc-result_app.asp?fldNOA=11-0513.04&BasicSearch=Go&Classification=0%2CUnknown+%2F+Unselected%2C1&applicantlist=0&categorylist=0&subcategorylist=0&materiallist=0&impactlist=0&fldMDPP=0.00&fldMDPN=0.00. (back to top)

Josh Brown has been in the dock and door industry for the last 13 years. He represented two dock equipment lines for six years, and has been managing TKO Dock Door sales for the last seven. Brown can be contacted by e-mail at sales@tkodoors.com.

To read the sidebar, “Impactable Dock Doors: Florida Building Code (FBC) 1715.5.3, ‘Exterior Door Assemblies,’” click here.

Impactable Dock Doors: Florida Building Code (FBC) 1715.5.3, “Exterior Door Assemblies”

by Josh Brown

Exterior door assemblies not covered by Florida Building Code (FBC) 1715.5.2, “Exterior Windows, Siding, and Patio Glass,” or FBC 1715.5.3.1, “Exterior Door Assemblies,” shall be tested for structural integrity in accordance with Procedure A of ASTM E330, Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylight,s and Curtain Walls by Uniform Static Air Pressure Difference, at a load of 1.5 times the required design pressure load. The load shall be sustained for 10 seconds with no permanent deformation of any main frame or panel member in excess of 0.4 percent of its span after the load is removed. The design pressures, as determined from American Society of Civil Engineers (ASCE) 7, Minimum Design Loads for Buildings and Other Structures, are permitted to be multiplied by 0.6. High-velocity hurricane zones (HVHZ) must comply with Testing Application Standard (TAS) 202. After each specified loading, there must be no glass breakage, permanent damage to fasteners, hardware parts, or any other damage that causes the door to be inoperable.

The exceptions include:

  1. Door assemblies installed in nonhabitable areas where the door assembly and area are designed to accept water infiltration, need not be tested for water infiltration.
  2. Door assemblies installed where the overhang (OH) ratio is equal to or more than 1 need not be tested for water infiltration. The overhang ratio shall be calculated by the following equation:

OH ratio = OH Length/OH Height where:
OH Length = The horizontal measure of how far an overhang over a door projects out from the door’s surface.
OH Height = The vertical measure of the distance from the door’s sill to the bottom of the overhang over a door.

1715.5.3.1 Sectional garage doors and rolling doors shall be tested for determination of structural performance under uniform static air pressure difference in accordance with American National Standards Institute/Door and Access Systems Manufactures Association (ANSI/DASMA) 108, Standard Method for Testing Sectional Garage Doors and Rolling Doors: Determination of Structural Performance Under Uniform Static Air Pressure Difference, ASTM E330’s Procedure A, or TAS 202. For products tested in accordance with ASTM E330, testing shall include a load of 1.5 times the required design pressure load sustained for 10 seconds, and acceptance criteria shall be in accordance with ANSI/DASMA 108. (HVHZ shall comply with TAS 202.)

Design pressures shall be determined from Table 1609.7(1) or ASCE 7. The design pressures, as determined from ASCE 7, are permitted to be multiplied by 0.6.

The Miami-Dade County Building and Neighborhood Compliance (BNC) Department set out to ensure the strictest standards for manufacturers, including those for the overhead sectional doors used at many warehouse and distribution facilities. These standards require a notice of acceptance and completion of:

  • air pressure test;
  • large missile impact test;
  • cyclic wind pressure loading test; and
  • a forced entry test.

To read the full article,”Impactable Dock Doors Help Increase Safety in Warehouses,” click here.

Structural Safety of Wood Decks and Deck Guards: Multi-family Balconies

by Joseph R. Loferski, PhD, and Frank E. Woeste, PE, PhD

Multi-family balconies are often framed with cantilevered wood, with a concrete covering and gypsum or vinyl ceiling. Structural drawings for a project typically contain a note describing the quality of lumber materials assumed and used by the structural engineer in the structural design process. For example, a materials note may read:

All framing lumber shall be No. 2 (minimum) D-FIR (or HEM-FIR) S-Dry.

S-Dry means at the time the lumber was surfaced (or planed) at the sawmill, the maximum moisture content (MC) of the individual lumber pieces was less than 19 percent. When structural engineers use a typical lumber note as presented, the intent is more inclusive than simple stating the MC of the product when manufactured, but it includes the assumed maximum MC of the lumber for the service life of the project (e.g. 50 years or more). The validity of their structural designs is conditioned on the assumption the lumber components will be protected from high MC conditions above 19 percent and liquid water.

‘Dry’ lumber that remains dry in-service is known to perform for centuries. It is a biological fact that manufactured ‘dry’ lumber that is exposed to liquid water, either continuously or intermittently, will absorb water and trigger the decay process. When lumber and lumber connections (i.e. nails, screws, and bolts) experience decay, they can no longer be relied on to function in-service as expected.

For the technical reasons cited, it is absolutely critical for the entire balcony and interface with the primary structure to be protected by a waterproofing system that protects all water exposed surfaces. For example, a guard system design detail may show a connection of the guard post to the outside balcony side(s). If the balcony sides are not protected from water entry, the guard system connections to balcony framing may be compromised due to hidden decay of the wood products.

In conclusion, waterproofing design/detailing by a professional is critical to the likely in-service performance of a balcony and balcony-structure interface. Further, field inspection of the waterproofing installations for strict conformance with the waterproofing details by the responsible design professional is recommended.

To read the full article, click here.

Structural Safety of Wood Decks and Deck Guards

Photo © BigStockPhoto/LeeBarnwell

Photo © BigStockPhoto/LeeBarnwell

by Joseph R. Loferski, PhD, and Frank E. Woeste, PE, PhD

Most residential deck-related accidents are caused by failure of the deck-to-house connection or of the guardrail system, which can cause a person to fall from the deck, resulting in serious injuries or death.

A sample of accident reports is given in Figure 1. Additionally, the authors have partial data dating back to 2001, showing the problem is widespread; accidents occur in nearly every region of the United States. The news reports often state the cause of a catastrophic deck failure was ‘over-loading.’ Based on media reports and the authors’ own investigations, however, many of the subject decks should have safely carried their load without collapsing.

Several media reports showing a sampling of deck collapses in the United States.

Several media reports showing a sampling of deck collapses in the United States.

Why do some decks and guards fail and cause injuries? Several reasons for deck failures have been observed, including inadequate fasteners and connections, corrosion, improper materials, construction defects, and wood decay.

Decks are often designed as a collection of individual parts, rather than as a unified system of interrelated components. For example, the failure of the deck ledger connection to the house may be due to a combination of factors, including no or improper flashing leading to decay in the house band joist, and improper or inadequate fasteners. Guard failure is most commonly caused by failure of the connection of the guard post to the deck, the connection of the rails to the post, or connection of the pickets to the rails. Further, because decks are exterior structures permanently exposed to weather, long-term decay or fastener/connector corrosion is more likely, and can contribute to a failure.

This article specifically addresses residential decks, but multi-family and light commercial decks, balconies, and guards—with more demanding code requirements—can have similar failure modes, making the general concepts quite pertinent. The architect and specifier should exercise great care and diligence when specifying deck or balcony-type structures (and related guards) as they are likely to require expertise in waterproofing specifications and details. (See “Multi-family Balconies.”)

Problem overview
Deck collapses and guard failures generally can be traced to designers and contractors who focus on parts and components rather than taking a holistic approach. For example, a through-bolted connection between the guard post and the deck band joist rarely fails. However, the connection of the band joist to the deck joist often uses nails or screws inserted in the end-grain of the joists. Since the guard post is at least 914 mm (36 in.) above the deck surface, it acts as a lever, causing the band joist to ‘peel’ away from the joists.

Photo of a typical deck attached to house; the circle shows the ledger connection. [CREDIT] Photos courtesy Joseph Loferski

Photo of a typical deck attached to house; the circle shows the ledger connection. Photos courtesy Joseph Loferski

The 2012 International Residential Building Code for One- and Two-family Dwellings (IRC) does not include a prescriptive method or detail for connecting a guard post to a deck substructure. Therefore, many contractors are faced to determine what is needed for a safe guard post connection without any code guidance, except for the vague 890-N (200-lb) concentrated load requirement in IRC.

Specific language and prescriptive details in a future IRC edition on how to make a connection of the guard post to the deck that will safely resist this 890-N load is desperately needed by all parties involved—specifiers, architects, engineers, contractors, home inspectors, and the building code enforcement community.

IRC does contain prescriptive guidelines for bolt and lag screw attachment of deck ledgers to a solid-sawn house-band, based on work by the authors at Virginia Tech University in collaboration with researchers at Washington State University.1

Deck ledger testing at Virginia Tech showing load application and deflection measurement made with a LVDT.

Deck ledger testing at Virginia Tech showing load application and deflection measurement made with a LVDT.

Design considerations for ledgers
Most often, decks are attached directly to the house using bolts or lag screws that connect the ledger to the house-band. On the other side, the deck is supported by a beam resting on columns bearing on concrete footings as shown in Figure 2.

Deck ledger connection tests were conducted to develop bolt and lag screw spacing requirements for various commonly used deck designs.2 Figure 3 shows a deck ledger connection being tested for gravity load capacity. The test used a 2×10 (nominal) to simulate the house band and a 2×8 (nominal) pressure-preservative-treated (PPT) member to simulate the deck ledger. Two simulated deck joists were attached to the ledger. The load was applied to the joists until failure. A transducer measured the ledger’s deflection relative to the band joist.

The results were used to compute fastener spacing requirements based on tested capacity of the connection. IRC Table R507.2 (Figure 4) gives the ledger connection requirements, and IRC Section R507.2.1 provides the required placement of bolts or lag screws in the deck ledger connection. All parties involved must closely review the design assumptions and limitations in the caption (e.g. live and dead loads) and footnotes to Table R507.2.1.

Proper screw and bolt installation requirements—American Wood Council’s (AWC’s) National Design Specification (NDS) for Wood Construction with 2012 Supplement—must be followed for the fastener spacing requirements listed in the table.

Data courtesy International Code Council

Data courtesy International Code Council

Another consideration is the type of lumber and posts used to build the deck. Using alkaline copper quaternary (ACQ) and copper azole (CAB) wood preservatives is now common for deck construction. These preservatives are generally known to be more corrosive to steel fasteners than chromated copper arsenate (CCA) preservatives. Therefore, corrosion-resistant fasteners such as hot-dipped galvanized steel or stainless steel must be used for reliable performance.

Some decay fungi are ‘copper limited,’ meaning they can colonize wood products treated with copper-based preservatives such as ACQ and CAB.3 Research has shown even wood treated to ‘ground contact’ treatment retention levels may experience fungal decay.4 So, embedding support posts into the ground may not be the best option. To improve deck post longevity, posts should be placed on concrete piers above ground-line and connected with a corrosion-resistant post-connector to the concrete piers. While not necessarily a code requirement, 6×6 (minimum) posts are recommended for aesthetic reasons and are much less likely to undergo severe warp (i.e. bow and twist).

Typical deck guard system showing posts, rails, and pickets. [CREDIT] Photo courtesy Joseph Loferski

Typical deck guard system showing posts, rails, and pickets. Photo courtesy Joseph Loferski

Properly installed flashing between the deck and house to prevent water infiltration into the wall sheathing and house band is extremely important. The typical house band joist (or engineered rim board) is not made from PPT lumber. Therefore, water intrusion into the wall section can lead to wood decay around the bolt or lag screw and thus failure of the connection. Proper flashing and caulking is needed to keep the house band dry, preventing decay. Due to the difficulty of achieving a reliable waterproofing system, a PPT house band—with compatible corrosion-resistant fasteners—at the deck attachment location is recommended.

Other system considerations include lateral bracing for both house-attached and freestanding decks. In Section R507.2.3 and Figure R507.2.3, IRC includes a prescriptive detail that can be used to meet the code requirements for lateral deck stability. The detail shows a connection from the deck joists to the house joists, and it requires a design load capacity of 6.67 kN (1500 lb). At least two such connectors are required for the deck’s lateral bracing.

Considerations for safe deck guards
A guard is a system of interconnected parts that protects occupants from falling off the deck for whatever reason. Guards are required on residential decks more than 762 mm (30 in.) above ground level. Per IRC, the guard must be 914 mm (36 in.) above the deck surface or, in the case of a bench-guard combination, the guard height must be 914 mm above the bench seating surface.

Wooden guards typically consist of many parts fastened with bolts, screws, or nails. Guard posts are typically stress-rated 4x4s bolted to the deck band joist. Two rails between the posts are usually 2×4 cross sections—one at the top of the post, and the other positioned less than 102 mm (4 in.) above the deck surface. The rails transmit the applied loads to the posts. Pickets between the rails transmit loads into the rails. A typical guard is shown in Figure 5. While not addressed in this article, numerous non-structural requirements for guards are extremely important to child and life safety, and are covered by IRC.

Tests of guardrail post to deck connections at Virginia Tech demonstrated a safety factor of 2.5 on the code required load of 890 N (200 lb). [CREDIT] Photo courtesy Frank Woeste

Tests of guardrail post to deck connections at Virginia Tech demonstrated a safety factor of 2.5 on the code required load of 890 N (200 lb). Photo courtesy Frank Woeste

The well-known building code requirement for guards is 890 N (200 lb) concentrated load applied in any direction to the top of the guard system. As stated earlier, a critical connection is the guard-post-to-deck structure. Laboratory tests of 4×4 posts loaded at 914 mm above the deck surface demonstrated the large force that is produced at the base of the post. Some commonly observed post connection details that rely on lag screws alone have been tested at Virginia Tech. For one tested case, the guard post separated from the deck band joist at a load level approximately 25 percent of the code requirement.

Due to the ‘lever’ action, the band joist can also separate from the joist ends because it is inadequately attached with nails or screws installed into the end grain of the joists.5 This connection detail is weak because the fasteners used to attach the band to the joists are loaded in withdrawal from end grain. The guard post is through-bolted to the deck band joist, so it appears to be a strong connection—however, it can fail at very low loads compared to what is required by the code.

Laboratory tests of 4×4 stress-rated guard posts (Figure 6) demonstrated steel connectors can adequately transmit loads produced by the code-required concentrated load on the top of the guard into the deck joists.

Figure 7 shows a schematic of a post-to-deck attachment using one or two connectors. For guardrails running perpendicular to the joists, the post can be attached directly to the connector if the post location is adjacent to a joist. Otherwise, two connectors are used to attach the band to joists, and the guard post is attached to the band with bolts between the connectors.

Schematic of post-to-deck attachment with connectors. [CREDIT] Image courtesy American Wood Council

Schematic of post-to-deck attachment with connectors. Image courtesy American Wood Council

When installing guards, one must also consider how rails are attached to the posts and the pickets to the rails. A preferred method is to attach the rails to the inside face of the posts with screws or threaded nails. The pickets are attached to the rails with screws or threaded nails. In no case should guard components be connected with smooth-shank nails, as the connection design strength is reduced by 75 percent due to in-service moisture changes.

Severely weakened post notched at the bottom. [CREDIT] Photo courtesy Joseph Loferski

Severely weakened post notched at the bottom. Photo courtesy Joseph Loferski

Guard posts should not be notched. In the past, bottom-notched posts were commonly employed to allow the post notch to sit on the deck surface, as shown in Figure 8. This practice severely reduces the post’s bending strength, and notching can worsen as cracks travel up from the corner of the notch.6

For all fasteners and connectors used in exterior environments, corrosion is an issue since it reduces connection strength. Therefore, at a minimum, code-recognized and approved corrosion-resistant metals or coatings must be employed in guard construction. Stainless steel fasteners and connectors are recommended by AWC DCA 6, Prescriptive Residential Deck Construction Guide, for guard systems exposed to saltwater or coastlines.7

 

 

Notes
1 For more, see the authors’ co-written article with D. Carradine and D. Bender in the May 2008 issue of Structure Magazine, “Lessons Learned: Residential Deck Ledger Connection Testing and Design.” Visit www.structuremag.org/Archives/2008-5/C-LessonsLearned-DeckLedger_Carradine-May08.pdf. (back to top)
2 See the authors’ co-written article with R. Caudill, T. Platt, and Q. Smith, “Load-tested Deck Ledger Connections,” in Journal of Light Construction (vol. 22, no. 6). Visit www.jlconline.com/Images/Practical%20Engineering_%20Load-Tested%20Deck%20Ledger%20Connections_tcm96-1098165.pdf. (back to top)
3 See the article by Loferski et al, “Brown-rot Decay of ACQ and CA-B Treated Lumber,” in Forest Products Journal (vol. 57, no. 6). (back to top)
4 Ibid. (back to top)
5 See the authors’ co-written article with D. Albright and Caudill, “Strong Rail-post Connections for Wooden Decks,” in Journal of Light Construction (vol. 23, no. 5). Visit www.jlconline.com/lumber/strong-rail-post-connections-for-wooden-decks.aspx. See also the co-written article with Albright from the July 2007 Structure Magazine, entitled “Tested Guardrail Post Connections for Residential Decks: Lessons Learned.” Visit www.structuremag.org/Archives/2007-7/C-LL_Wood_Post_Connections_by_Loferski.pdf. (back to top)
6 Ibid. (back to top)
7 See Woeste’s article, “Safe and Durable Coastal Decks,” from Coastal Contractor (vol. 5, no. 2). Visit www.coastalcontractor.net/pdf/2008/0803/0803safe.pdf. (back to top)

Joe Loferski, PhD, is a professor of sustainable biomaterials at Virginia Tech. He has an international reputation and experience in the areas of performance of wood and wood composites in buildings, along with the preservation of historic wood buildings. Loferski can be reached at jloferski@vt.edu.

Frank Woeste, PE, PhD, is an adjunct professor of sustainable biomaterials at Virginia Tech. He is a wood construction and engineering consultant, and a past contributor to The Construction Specifier. Woeste can be contacted via e-mail at fwoeste@vt.edu.