Patent Application
20080168726
This invention relates to protective covers for exposed steel reinforcing bars used in reinforced concrete.
Steel reinforcing bars (“rebar”) are used in reinforced concrete in building structures. During the construction of buildings, the ends of the rebar are often exposed and extend upwardly from recently poured concrete sections or walls. Exposed ends are sharp and present a hazard to workmen, particularly to workmen working overhead. Many workmen have sustained puncture injuries, and in a significant number of cases have been killed, due to accidentally falling or stepping onto the exposed ends of the rebar.
Various protective safety covers have been proposed and used to protect workmen from this hazard. Bush U.S. Pat. No. 4,202,378 and Bush Design Pat. No. 262,093 refer to a protective safety cover for use on the free projecting ends of rebar comprising a hollow cylindrical body of a deformable plastic material, the body being closed at one end and open at the other. A plurality of inwardly extending projections are formed within the open end of the cylindrical body to secure the protective cover to the rebar. The closed end of the body has a flat circular head which extends radially outwardly from the body to present an enlarged flat impact surface. Other plastic protective covers for rebar are discussed in Schimmelpfenning U.S. Pat. No. 5,884,443 and Don De Cristo Concrete Accessories Inc. Catalog “Plastic Rebar Guard”, p. 43. Lunn U.S. Pat. No. 4,833,850 proposed a protective cover for rebar in the form of a metal support adapted to hold a impact absorbing spherical cushion.
When it was realized that these all plastic protective covers were subject to penetration upon severe impact, such as a workman falling from a height, it was proposed to insert a separate piece of rebar through lateral holes near the closed end of the cylindrical body to provide for a steel stop as discussed in WO91/14839 and Underwood U.S. Pat. No. 5,363,618. This approach is not self-contained, is inconvenient, and subject to not being consistently practiced.
Consequently, protective covers having a built in metal plate or “seat” in the bottom of the closed end of the body were developed. Protective covers of this type are discussed in Schnepf U.S. Pat. No. 5,313,757, Workman U.S. Pat. Nos. 5,447,290 and 5,613,336, Deslauriers Impalement Protective “Safety Cap DISC System”, Buffalo American Allsafe Company “BarGard”, Mutual Industries Inc. OSHA Rebar Cups Part Numbers 14640-4 and 14640-5, Dunn U.S. Design Pat. No. 408,268, and Kassardjian et al U.S. Pat. Nos. 5,381,636, 5,523,043, 5,568,708, 5,824,253, 5,943,836, 5,946,871 and Design No. 363,657. Protective covers with metal plates or seats passed the original Cal OSHA drop test.
However, after an investigation of job site injuries, Cal OSHA subsequently declared that the existing protective covers with metal plate or seat were inadequate, primarily due to being subject to penetration through the side of the cylindrical body upon impact on the head, resulting in serious puncture injuries to workmen falling onto the rebar.
Cal OSHA since established a new and more stringent drop test which all new rebar protective covers are required to meet. Kassardjian et al U.S. Pat. No. 5,729,941 relates to a rebar cover having a preformed metal stamping in the form of a bowl-shaped metal seat which is incorporated in the closed inner end of the cylindrical body. The bowl-shaped metal seat is said to be of a composition and thickness to prevent penetration of the rebar through the seat and thereby preclude penetration of the rebar through the side of the cover body upon impact.
The use of a preformed bowl-shaped metal stamping as the seat adds to the expense of the rebar protective cover.
Subsequently, a rebar protective cover having a hollow cylindrical body and impact head of a thickness and integrally formed of a plastic material was developed which was found to provide a protective cover which passes the current Cal OSHA drop test. This rebar protective cover is disclosed in applicant's co-pending U.S. patent application Ser. No. 09/569,826, filed May 12, 2000, the disclosure of which is incorporated herein by reference.
Briefly, this invention comprises a rebar protective cover for use on the projecting free end of a concrete reinforcing bar to prevent impact injuries comprising:
The invention further comprises the combination of a rebar used to reinforce concrete wherein the rebar has an exposed free end and a safety protective cover disposed on said exposed, said protective cover comprising:
Turning to the drawings:
The hollow cylindrical collar 2 is closed at one end 6 and is open at the other 7. The flat impact head 1 is formed so that when joined to the cylindrical collar 2, the impact head extends beyond and overhangs the collar 2.
The separately formed impact head 1 as shown is preferably circular and has an area of about 16 square inches as required by Cal OSHA. The impact head can also be square.
Four web-like buttresses 8, spaced at a 90° interval, help support the periphery of the impact head 1 around its underside.
The fin holder 5 has the inside flanges 9 serve to keep the protective cover longitudinally aligned with the rebar 10 by gripping the sides of the rebar.
The fin holder 5, the shaping member 4, the collar 2 and the impact head 1 are first individually formed by injection molding of the polyolefins described herein.
Then the putty-like cement is poured into the collar 2 in an amount sufficient so that when the shaping member 4 is inserted, the cement rises to about mid-level inside the collar 2 as shown in
The fin holder 5 is then placed in the collar 2 and the impact head 1 positioned against the closed end 6 of the collar 2. The assembly is heated to cause the fin holder 5 to adhere to the inside of the collar 2 and the impact head 1 to adhere to the closed end 6 of the collar 2. This assembly can be performed before or after the cement 3 has hardened. Complete hardening of the cementitious material 3 takes about 24 hours. The shaping member 4 becomes adhered to the surface of the hardened cement 3.
In the completed protective cover, the shaping member 4 is preferably positioned such that the top of the shaping member is about midway between the closed end 6 of the collar 2 and open end of the collar and the concave bottom surface of the shaping member 4 is about one third the distance from the closed end 6 of the collar to the open end of the collar 2. A preferred example of these dimensions is shown in
The plastic parts of the protective cover of this invention are integrally molded, in standard plastic injection molding equipment, using a high molecular weight polyolefin polymers. The plastic can contain a small amount (about 0.04%) of an orange colorant such as anti-UV red, a small amount of orange pigment (about 0.032%) and a small amount of filler such as calcium chloride (about 1% to 3%), all based on the total weight of polymers. These additives are desirable, but not essential.
In my preferred embodiment, the plastic parts of the protective cover are injection molded of a homogenous mixture of two very high molecular weight polyethylene polymers as follows:
The upper limit of the molecular weight of the ultra high molecular weight high density polyethylene is not critical. Such polymers currently available are believed to be only slightly above 15×105 but could be higher such as 20 or 25×105.
The two polymers are premixed and colorant, pigment and filler are added. A homogenous blend forms in the molten state which is then injected into the cavity of the mold. Injection molding equipment is used to form the protective cover to the desired shape.
The cementitious portion of the protective cover is a high strength concrete mixed with carborundum/ceramic grain.
The cementitious portion 3 of the protective cover is prepared by mixing:
These ingredients are mixed with water. Various well known cement additives can also be added in minor amounts. Those skilled in the art can modify the ingredients and proportions.
The following are preferred ingredients:
1. The carborundum particles size: about 8-20 mesh
2. The quartzite particles size: about 40-50 mesh
3. Ceramic powder: composition is Al2O3, SIO2 and MgO
4. Ceramic powder particle size: 40-50 mesh.
The upper surface of the impact head 1 of the protective cover is preferably flat as shown in the Figures. However, a domed or mushroom shaped upper surface is also acceptable.
The original Cal OSHA drop test required the protective cover be capable of withstanding at least the impact of a 250 pound weight dropped from a height of 10 feet without penetration failure of the cover. This drop test was based on the rebar being aligned with the longitudinal dimension of the cylindrical body portion.
The problem is that many prior protective covers in actual use, upon impact, allowed the rebar to penetrate and pierce the side of the cylindrical body at or around its junction with the impact head. Failures of this kind have resulted in serious industrial accidents.
Since it was found upon severe impact that the interior flanges 9 would break or give way, allowing the protective cover to become cocked at an angle to the rebar, the latest Cal OSHA drop test requires that it be conducted with the protective cover positioned over the rebar as shown in
The following test results demonstrated the efficacy of the rebar safety protective cover of this invention.
A rebar protective cover was assembled using as the cementitious material a mixture of carborundum about 75%, cement about 24% and quartzite about 1%, all of weight.
The drop test was conducted in accordance with the latest Cal OSHA procedure. The rebar protective cover of
The rebar caps completed the drop tests with no evidence of cracking and/or splitting of the cementitious material.
As used herein, the term “Cal OSHA drop test” refers to the above described test.
These results indicate that the rebar protective cover of this invention is likely to be more effective in preventing serious puncture injuries to workmen accidentally falling on the end of exposed rebar.
