Structures Design Guidelines | Jan 2009
3 - Substructure and Retaining Walls |

## 3.14 Fender Systems (01/06) 2006 Jan: Added New Section "Design Criteria.'

### 3.14.1 General

A. The FDOT standard bridge fender systems serve primarily as navigation aids to vessel traffic by delineating the shipping channel beneath bridges. The fender systems are designed to be robust enough to survive a multitude of bumps and scrapes from barge traffic, and to absorb kinetic energy while redirecting an errant barge or other vessel.

B. Dolphins and islands can be used to protect existing bridge substructures that were not designed to resist vessel collision loads and in some cases are used to protect the substructures of bridges located at port facilities. Typically the use of dolphins and islands is discouraged as they also represent a hazard to vessels, aggravate scour and increase water flow velocities. Dolphins and islands will require customized designs and usually will include extensive hydraulic and geotechnical evaluations.

### 3.14.2 Responsibility

A. The Department determines when fender systems or other protective features are required and requests U.S. Coast Guard concurrence with plan details and locations.

B. Coordination with the Army Corps of Engineers and local government agencies is also encouraged as they may have plans that could affect the channel alignment/depth and/or type/volume of vessel traffic.

### 3.14.3 Procedure (01/09) 2009 Jan: Added additional criteria "...the navigation channel is centered on the span,..." in Paragraph A.

A. The majority of bridges over navigable waterways in Florida under the jurisdiction of the USCG will require an FDOT standard fender system. In some cases, circumstances such as deep water, poor soil conditions and /or heavy vessel traffic will lead to long span designs. If the bridge span is approximately 2.5 times the required navigation channel and the navigation channel is centered on the span, omit a fender system unless required by the USCG. Each bridge site is unique and the USCG will evaluate the Department’s plans based on local characteristics such as accident history, water velocities and cross currents, geometry of the channel, etc. If a fender system is omitted, a conservative approach should be taken with respect to the minimum pier strength requirements as developed with the Vessel Collision Risk Analysis.

B. Selection of fender system:

1.) The Heavy Duty and Medium Duty Fender Systems are intended to be used only where steel hulled commercial barge traffic exists. The Light Duty Fender System may be used for very low volume commercial traffic and other vessels.

2.) Consider site conditions, past accident history, volume and size of vessel traffic and bridge main span length relative to channel width when selecting a fender system.

3.) As guidance, the following is recommended:

a.) Heavy Duty - channel pier strength requirement from risk analysis exceeds 2500 kips.

b.) Medium Duty - channel pier strength requirement from risk analysis 1000 to 2500 kips.

c.) Light Duty - minor commercial traffic, pier strength requirement less than 1000 kips.

### 3.14.4 Design Criteria Used to Develop the Standard Fender System (01/07) 2007 Jan: 3.14.4 B3 - Revised applicability of the standard fender design and defined design assumptions. 2006 July: Revised 3.14.B. 2 to clarify pile top at 24-feet above soil with N>6 blow count. Added 3.) for custom design.

A. The standard fender systems are designed as flexible, energy absorbing structures. It is expected that this type of design will minimize the potential for damage to vessels and fenders during a minor collision while being able to redirect some vessel impacts that would otherwise destroy a more rigid style fender system.

B. The basic design methodology is described in sections C3.8, C3.9 and C7.3.1 of the 1991 AASHTO Guide Specifications and Commentary for Vessel Collision Design of Highway Bridges, and the following:

1.) A trial fender system is designed. A series of ever increasing static forces are applied to the critical location on the fender. A force versus displacement diagram is developed from the analysis and the area under the force/displacement diagram is computed (the maximum force being the static force which creates yielding of fender material). This area represents the fender system energy available to redirect or possibly bring an errant vessel to rest. With this system energy determined, the critical speed at which a vessel would fail the fender system can be calculated based on an assumed vessel size and approach angle.

2.) The basis for determining the pile tip elevation was to maintain a safe embedment (Ef) or locate it ten feet below the 100-yr storm scour, whichever is greatest. To verify stability, a computer program that allows modeling a single cantilever pile embedded in weak soil incorporating soil strengths using P-Y curves was employed (FBPIER , LPILE). The top of the pile was loaded 24 feet above soil having a blow count greater than 6 (N>6) with a transverse load that generated the pile yield moment. The pile tip elevation was raised until pile deflections, especially at the pile tip, became unreasonable. It was assumed that the unstable embedment (Eo) is one foot greater than the embedment that caused unreasonable deflections. An additional embedment of 5 feet or 20% of the unstable embedment (Eo), whichever is greater, was then added to Eo to determine the safe embedment (Ef).

3.) The Fender System shown in the Design Standards, 21900 Series, can be used at locations where water depth, at mean low water, plus depth of soil having N values < 6 does not exceed 30 feet. Depths greater than 30 feet require design calculations and coordination with the appropriate structures office to insure yield moments and reasonable deflections are not exceeded. In addition, a constructability review including manufacturing, transportation and installation is required. The following pile length assumptions were used in the design of the fender system:

a.) Pile top is 8 feet above MHW

b.) Embedment of 24 feet into soil having a blow count (N) greater than 6.

c.) Channel depth of 30 feet. This includes soil/mud height which has a blow count (N) less than 6.

d.) Tidal change of 4 feet. (MHW-MLW=4'). If the actual tidal variation (MHW-MLW) is less than 4 feet, the allowable channel depth may be increased by the difference between the assumed tide of 4 feet and the site specific tide.

C. Energy Capacities and Sample Design Vessels (all samples assume 15 degree approach and friction coefficient = .15)

1.) The “Heavy Duty” plastic fender system, Design Standard 21910.

a.) Energy capacity 295 ft-kips.

b.) Two loaded jumbo hopper barges + push boat at 4.0 knots.

c.) Two empty jumbo hopper barges + push boat at 9.8 knots.

2.) The “Medium Duty” plastic fender system, Index No. 21920.

a.) Energy capacity 132 ft-kips.

b.) One loaded jumbo hopper barge + push boat at 3.6 knots.

c.) One empty jumbo hopper barge + push boat at 7.8 knots.

3.) The “Light Duty” concrete pile with plastic wales system, Index No. 21930.

a.) Energy capacity = 38 ft-kips.

b.) One empty jumbo hopper barge + push boat at 4.2 knots.

c.) One push boat at 5.6 knots.

### 3.14.5 Miscellaneous Considerations (01/06) 2006 Jan: Revised to permit plastic piles.

A. The fenders should flare at the same points directly opposite each other measured perpendicular to the centerline of the navigation channel. Ten feet is the minimum distance from the superstructure coping to the beginning of the fender flare. Typically one of the currently available three standard fender systems is to be utilized unless directed otherwise by the FDOT.

B. At some freshwater sites with light vessel traffic, treated timber piling may be used. This will require a site specific design.

C. Where requested by the District Structures Maintenance Engineer, ASTM A 709, Grade 36 steel piling may be used to support the fender system. This will require a site specific design.

D. If custom fender designs are used, pile clusters shall be wrapped with polypropylene impregnated wire rope in accordance with FDOT Spec 936, Wire Rope For Fender Pile Cluster.

E. Pile Length Determination: The minimum pile embedment depths are 20 feet for concrete piles or 24 feet for plastic piles into soil having a blow count “N” greater than or equal to 6 or 10 feet below the 100 year scour elevation, whichever is greatest. The pile length is the embedment length plus the distance to the pile head which is set at a minimum of 8 feet above NHW or MHW.

F. A Pile Installation Constructability Review must be performed by the Geotechnical Engineer to verify that the pile tips shown in the plans can be reasonably obtained by the Contractor, and the use of any penetration aids (jetting, preforming, etc.) will not jeopardize adjacent structures.

G. Investigate and resolve conflicts between the proposed fender system and existing utilities or structures.

H. Design system with timber or concrete piles or plastic piles.

I. Design with wood or plastic wales. Substitute plastic wales for wood wales on a one-to-one basis. Use either 10-inch x 10-inch or 12-inch x 12-inch sizes.

J. Fender piles generally have a short life expectancy, are considered sacrificial, and no corrosion protection is required beyond the use of concrete class as shown in Table 1.3.

### 3.14.6 Ladders and Platforms

A. Contact the District Structures Maintenance Engineer for ladder, platform, and catwalk requirements.

B. Design ladders and platforms per OSHA CFR Title 29,Part 1910, Section 27.

C. Where fender lighting maintenance access is not provided by boat, provide OSHA compliant handrails on walkway leading to fender catwalk.

D. For bridges and fender systems, specify steel or other accepted metals for ladders.

E. The clearance between rungs and obstructions should be 12-inches but not less than 7-inches (OSHA minimum.)

### 3.14.7 Navigation Lighting Details

A. Bridges over waterways with no significant nighttime navigation may be exempted from lighting requirements by the proper authorities; however, most bridges over navigable waterways will require some type of lighting. Refer to Code of Federal Regulations (CFR) 33 Part 118.

B. For navigation lighting requirements, see the USCG Bridge Lighting and Other Signals Manual.