IMPACT RESISTANT COMPOSITE METAL STRUCTURE

Abstract

An impact resistant composite metal structure (IRCMS) loaded by static and dynamic loads has high-strength reinforcing elements embedded in a ductile base member. The present invention gives an opportunity to utilize plastic property of base members in order to increase impact resistance and strength-to-weight ratio of the composite metal structures. The present invention can be applied to building and bridge construction, automotive industry, mining equipment, ship and plane construction; anywhere a structure works under conditions of substantial dynamical forces.

Description

BACKGROUND OF THE INVENTION

The present invention relates to the structures working under conditions of accidental natural dynamic forces or dynamic loads caused by moving structure (for example, truck, plane or ship) or moving subjects on structure (for example, bridge). Such structures are exposed to bending, compression and tensile stress should have a high capacity in combination with sufficient ductility to remain structurally safe when forced into an inelastic range in a major earthquake.

Increasing ductility of the structure leads to a decrease in the effect of dynamic loads and an increase in the impact resistance of a structure without sustaining significant damage. Different approaches are currently used in the industry to increase impact resistance of structures used in dynamic environments. Some of the approaches are related to a connection of members in the frame construction of buildings. For example: Reduced Beam Section (RBS), Free Flange Connection (FF), Welded Unreinforced Flange (WUF) etc. [See: Seismic Provisions for Structural Steel Buildings. AISC, May 21, 2002] and Seismic Structural Device [disclosed in U.S. Pat. No. 6,681,538] are widely used for Beam-to-Column connections.

These approaches, based on plastic hinges introduction, can protect connections of the members. However, the plastic hinges, increasing ductility, have decreased capacity of the middle span sections and accordingly decreased a strength-to-weight ratio. Also all of these approaches are involved extensive labor preparation in a field/workshop.

Reinforcement of the members of metal structure could be done with high-strength metal plates fixed on the flanges of a regular beam by welding or bolting. This approach is not effective because of brittleness of the high-strength metal and a high probability of loosing stability of the plates in a zone of compression stress especially in dynamic environments. Numerous modifications of composite metal structures are widely used in industry. For example, impact resistant composite metal castings used for protection of mining and construction equipment from abrasive wear. Some castings are disclosed in U.S. Pat. No. 5,328,776. They have a ductile base matrix where wear resistant elements, made of high strength steel or cast iron, are embedded. The ductile matrix base absorbs an impact load, creates an effect of confining pressure and protects the brittle wear resistant elements from direct impact loads. The wear resistant elements in these composite castings are short and they can not be used as a member of structure working under conditions of bending, compression and tensile loads.

Wide field of composite metal application is the MMC—Metal Matrix Composite. This composite was created to increase tensile strength and decrease weight for bare overhead electrical power in transmission cables (examples are disclosed in U.S. Pat. No. 6,723,451). It can not be used for structural members loaded by compression or bending dynamic load. Another structural composite material used in industry is FRP—Fiber Reinforced Polymer. The FRP have been used in aerospace and manufacturing applications, where low weight, high tensile strength and noncorrosive structural properties are required. The FRP was proven in civil engineering as composite strengthening system for wood, masonry and concrete structures (examples are disclosed in U.S. Pat. No. 6,599,632). However the effect of high strength of fibers can not be fully accomplished in composite structure because different mixtures of epoxy are used to fix the high strength fibers on the surface of the structures. Low strength of the epoxy glue compare with FRP and especially creep of the epoxy does not allow completely transfer the tensile stress from the structure to reinforcing elements made of the FRP. In compression stress zone effect of using the high strength FRP is even less than in tensile zone because of relaxation of compressive stress and loosing stability (local bifurcation) of FRP.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide increasing ductility and impact resistance of the structure without loosing its capacity, which avoids the disadvantages of the prior art.

In keeping with these objects and with other, which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in an impact resistant composite structure, which has a base member, and reinforcing elements, wherein the reinforcing elements are embedded in the base member in longitudinal direction below its surface or flush with it.

Until basic loads (dead load and live load) are applied, stresses in the base member and in the reinforcing elements are the same. At the time when dynamic loads are applied, the base member is deformed in plastic state, but the reinforcing elements continue to deform in elastic state for the same strain. This is the main effect of the present invention, which provides ductility of the structure and its structural stability under substantial dynamic/seismic loads. In addition, the effect of confining pressure, due to the embedded reinforcing elements, decreases their brittleness and risk of loosing stability in the compression zone.

Furthermore, using a composite metal structure with high-strength reinforcing elements according to the present patent mitigates impact damage and provides increasing the strength-to-weight ratio over conventional metal in seismic/dynamic environments.

The present invention gives an opportunity to utilize plastic property of base members in order to increase impact strength of structures. Metal of base members can withstand stresses beyond the yield stress without any fracture. However, according to traditional design practice this effect usually is not used and stress conditions are not allowed above the yield stress, because of the risk of loosing stability of compressed members or unlimited deformation of tensile or bended members without additional load.

For the present invention of composite structures, base members could be accepted completely in a plastic state. It gives the opportunity to increase ductility of the structure and high-strength reinforcing elements provide a guarantee of structural stability when seismic/dynamic loads are applied.

It is assumed that the strains in embedded reinforcing elements are the same as those of surrounding base member and the perfect bonding exists between the reinforcing elements and the base. The perfect bonding means that no slip can occur between the two materials. It can be achieved by using deformed reinforcing bars or by embedding the reinforcing elements below the surface of the base member.

The present invention can be applied to building and bridge construction, automotive industry, mining equipment, ship and plane construction, where structural members work under conditions of substantial dynamical forces.

The novel features, which are considered as characteristic for the invention, are set in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

DEFINITIONS

“IRCMS” is abbreviation for an Impact Resistant Composite Metal Structure. “Base member” means a beam or a column or a plate with all standards wrought rolling forms, including W-beam, channel, angle, structural tubing and pipe or can be assembled from the standard forms as a built-up section. The base members also can be manufactured by casting or extrusion of a metal. The base members made of ductile metal.

“Reinforcing elements” are substantially continuous deformed round bars, strands or elements with square, rectangular, triangular or trapezium shape of cross section or mesh made of metal with strength much higher than the strength of base member metal. The reinforcing elements have bosses on their surface in order to increase bonding between base member and reinforcing elements.

“Channels” are grooves made in base member for the installation of the reinforcing elements.

“Average effective diameter” means diameter of the circle of reinforcing element. The average effective diameter for irregular shape of cross section of the reinforcing element is calculated by formulae: $d=2*\sqrt{\frac{A_r}{\pi }}$

Where A_r

is area of cross section of the reinforcing element.

“Longitudinally positioned” means that reinforcing elements are oriented in the same direction as the length of the base member or around this member as helical arrangement, or with less or equal 45 degree of reinforcing elements in mesh with the base member direction.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings further describe the invention.

FIG. 1 is a cross-section of composite beam with square reinforcing elements.

FIG. 2 is a cross-section of composite beam with round and trapezium reinforcing elements.

FIG. 3 is a cross-section of composite pipe column with round reinforcing elements and exterior confining pipe.

FIG. 4 is a composite column with round reinforcing elements embedded on helical longitudinal arrangement.

FIG. 5 is phases of embedding of the reinforcing elements. a) milling the channels 4 in the base member 1, b) embedding the reinforcing elements 2 into the channels 4, c) pressing in the base member 1 and closing the channels 4.

DETAILED DESCRIPTION OF THE INVENTION

Composite metal structures in accordance with the present invention have a ductile base member 1 and high-strength reinforcing elements 2, which are embedded in the base member (see FIGS. 1 and 2).

Beams and columns from all standard wrought forms, including W-beam, channel, angle, plate, structural tubing and pipe can be used as a base member. Built-up sections also can be used as the base member. For the built up section the reinforcing elements are embedded in flange plates.

The base members can be made by using rolling, castings or extrusion process. The channels for installation of the reinforcing elements are made during the rolling or extrusion process and close out by pressing in right after the installation. For the casting process, the reinforcing elements are installed in mould for base member and a liquid metal is poured into the mould. The reinforcing elements can be also embedded into a cast and the structure with reinforcing elements is pressed or rolled under high pressure to increase bonding between two metals.

Deformed bars, strands, square, rectangular, triangular or trapezium shape of cross section can be used as the reinforcing elements. The reinforcing elements with triangular or trapezium shape of cross section are embedded with widest base of the reinforcing elements at the bottom of the channels. Preferred material for the reinforcing elements is a high-strength metal. The strength of the reinforcing elements shall be much higher than strength of the base member metal.

For the base member, made of metal pipe and loaded with eccentric compression loads, the reinforcing elements are equally distributed around external perimeter of the pipe and they are embedded in longitudinal direction flush by pressing in during a hot rolling or extrusion process. After cooling of the composite pipe with embedded reinforcing elements it is inserted into another hot pipe, having interior diameter (in hot condition) tittles more than exterior diameter of the composite pipe with reinforcing elements (see FIG. 3). The exterior pipe 3 after the cooling creates confining pressure on the composite pipe and increases its strength.

In order to increase ductility of the structure for condition of the strong impact, the reinforcing elements are embedded to the pipe in helical longitudinal arrangement (see FIG. 4).

Next step to increase capacity of the column made of pipes is recommended to fill out the interior pipe with concrete forming a Lally column.

The reinforcing elements are embedded flush with surface of the base member in tension zone (see bottom part on FIGS. 1 and 2) or in case of a small thickness of the base member in compression zone (less three effective diameters of the reinforcing elements). In this case deformed bars, strands, triangle or trapezium shapes of the reinforcing elements are recommended in order to increase bonding between the base member 1 and the reinforcing elements 2. The trapezium or triangle shapes of the reinforcing elements are recommended to embed with less width of the reinforcing elements at the base member surface. In order to have reliable bonding between base member and reinforcing elements, they are made with bosses or notches (similar to deformed bar) distributed around their surface in longitudinal direction.

If a thickness of the base member in compression stress zone is more or equal three effective diameters of the reinforcing elements the reinforcing elements are embedded below surface of the base member. The channels in the base member are milled directly before the reinforcing elements are embedded during the hot rolling or extrusion process, and the channels are pressed in directly after the reinforcing elements are embedded in the channels.

The reinforcing elements are embedded in channels 4 in the base member in the following three phases (see FIG. 5):

a) during a hot rolling or extrusion process the channels 4 are milling in the base member (see FIG. 5 a);

b) the reinforcing elements 2, having a room temperature, are embedded in channels 4 (see FIG. 5b);

c) channels 4 are closed by pressing in the base member directly after embedding the reinforcing elements 2 (see FIG. 5 c).

Sizes of cross section of the reinforcing elements and their embedded depth are selected depend on thickness of the base member. For most cases an effective diameter of the reinforcing elements is recommended equal from one fifth to one third of the base member thickness and the embedded depth is recommended in diapason of one quarter to a half of the base member thickness.

The less the thickness of the base member, the less sizes of the reinforcing elements and their embedded depth shall be used, up to flush the reinforcing elements with the base member surface. A mesh matrix of reinforcing elements is recommended in order to decrease an effect of dynamic load. Angles of the reinforcing elements in the mesh with longitudinal direction shall be less or equal 45 degree. The mesh of reinforcing elements could be used to wrap up pipe by pressing in the mesh into the pipe surface or pressing in the mesh into plate.

The reinforcing elements are spaced from one another by a distance that is a multiple of transverse size of the reinforcing elements and percent of area of the reinforcing elements from the total cross section area of the composite structure is recommended in a range of 3%-7.5%.

An example of the Impact Resistant Composite Metal Structure invention is presented herein below.

First, let's consider a traditional W-beam with span l=30 ft which is fixed at both end supports and loaded a concentrated load P at the center of the span.

Assume, for example, that: fy=60 ksi

yield stress for steel grade G60, E=29,000 ksi

modulus of elasticity, χ=3

• • dynamic factor M_y=20,000 k−in

maximum bending moment from loading of the beam, including dynamic loads

Required section modulus $\begin{array}{cc}{S}_x\mathrm{is}\text{:}{S}_x=\frac{M_y}{f_y}=\frac{20\text{,}000}{60}=333{\mathrm{in}}^3& \left(1\right)\end{array}$

Try a beam W18×175:

Area of cross-section A=51.3 in² , height of the beam d=20 in , web thickness t_w=0.89 in , flange thickness t_f=1.59 in , flange width b_f=11.38 in , moment of inertia I_x=3450 in⁴ , elastic section modulus S_x344 in³ , plastic section modulus Z_x=398 in³.

Capacity of the beam is: M_y=f_y×S_x=60×344=20,640 k−in and maximum of the dynamic load is: $\begin{array}{cc}{P}_d=8⨯\frac{M_y}{l}=8⨯\frac{20\text{,}640}{30⨯12}=460k& \left(2\right)\end{array}$

Equivalent static load is: $\begin{array}{cc}{P}_{\mathrm{st}}=\frac{P_d}{\chi }=\frac{460}{3}=153k.& \left(3\right)\end{array}$

Maximum displacement from the static load P_st in the middle of the span can be determined by formulae: $\begin{array}{cc}{\Delta }_{\mathrm{st}}=\frac{P_{\mathrm{st}}⨯l^3}{192⨯E⨯I}=\frac{153⨯{\left(30⨯12\right)}^3}{192⨯29\text{,}000⨯3450}=0.37\mathrm{in}& \left(4\right)\end{array}$

To simulate a dynamic loading, let's consider weight W=P_st=153 k falling on the beam from a height h

The dynamic factor in this case can be determined by known formulae: $\begin{array}{cc}\chi =1+\sqrt{1+\frac{2⨯h}{{\Delta }_{\mathrm{st}}}}& \left(5\right)\end{array}$ and for the given χand Δ_st , the height h

• • can be determined from the formulae: $\begin{array}{cc}h=\left({\left(\chi -1\right)}^2-1\right)⨯\frac{{\Delta }_{\mathrm{st}}}{2}=\left({\left(3-1\right)}^2-1\right)⨯\frac{0.37}{2}=0.56\mathrm{in}& \left(6\right)\end{array}$

Now let's consider the same beam with reinforcing elements according to the current invention. Try seven reinforcing bars, grade G270, f_yr=200 ksi , with square cross-section (0.5×0.5=0.25 in²) , embedded in the top flange on 0.25 in from the surface and flush at the bottom. As we discussed before, in case of using reinforcing elements, the beam (base member) can be accepted completely in plastic conditions. A capacity of the composite reinforced beam M_c can be determined by the following formulae: M_c=M_p+M_r=f_yZ_x+(f_yr−f_y)×A_r×a_r  (7)

Where M_p is a plastic bending moment, taken by the base member (beam) and M_y is a bending moment taken by reinforcing elements.

For the given f_y, f_yr, Z_x A_r=7×0.25=1.75 in² and a_r=d−0.5−0.25=20−0.75=19.25 in M_c=60×398+(200−60)×1.75×19.25=23,880+4716=28,596 k−in

The reinforcing of the beam increases its capacity compare with the regular beam for 38.5%: $\frac{M_c-M_y}{M_y}⨯100\%=\frac{28\text{,}596-20\text{,}640}{20\text{,}640}⨯100\%=38.5\%$

Now, let's find parameters of the reinforced composite beam, which has capacity equivalent to the regular beam M_y=20,640 k−in

Required section modulus of the composite beam is $S_{\mathrm{xc}}=S_x⨯\frac{M_y}{M_c}=344⨯\frac{20\text{,}640}{28\text{,}596}=247{\mathrm{in}}^3$

Try for the base member a beam W18×130:

Area of cross-section A=38.2 in² , height of the beam d=19.25 in , web thickness t_w=0.67 in , flange thickness t_f=1.2 in , flange width b_f=11.16 in , moment of inertia I_x=2460 in⁴ , elastic section modulus S_x=256 in³ , plastic section modulus Z_x=291 in³ a_r=d−0.75=19.25−0.75=18.5 in

The actual capacity of the reinforced composite beam can be determined by the formulae (7): M_c=60×291+(200−60)×1.75×(19.25−0.75)=21,992 k−in , which is more than required M_requred=20,640 k−in.

Limited strain for high-strength reinforcing elements is 0.007, which corresponds to modules of elasticity: $E_r=\frac{f_{\mathrm{yr}}}{\varepsilon }=\frac{200}{0.007}=28\text{,}571\mathrm{ksi}$

For steel grade G60 equivalent modulus of elasticity is: $E=\frac{f_y}{\varepsilon }=\frac{60}{0.007}=8571\mathrm{ksi}$

Ratio of the modules is $n=\frac{E_r}{E}=\frac{28\text{,}571}{8571}=3.33$

Equivalent moment of inertia for the composite section can be determined by: $I_{\mathrm{xc}}=I_x+2A_r\times \left(n-1\right)\times {\left(\frac{a_r}{2}\right)}^2=2460+2\times 1.75\left(3.33-1\right)\times {\left(\frac{18.5}{2}\right)}^2=2460+698=3158\mathrm{in}$

The static displacement in the middle of the span for the composite beam can be determined by formulae (4): ${\Delta }_{\mathrm{st}}=\frac{P_{\mathrm{st}}\times l^3}{192\times E\times I}=\frac{153\times {\left(30\times 12\right)}^3}{192\times 8571\times 3158}=1.37\mathrm{in}$

The dynamic factor χ

for the composite beam can be determined by formulae (5): ${\chi }_c=1+\sqrt{1+\frac{2\times h}{{\Delta }_{\mathrm{st}}}}=1+\sqrt{1+\frac{2\times 0.56}{1.37}}=2.35$

In comparison with regular beam, the composite beam has the following advantages: Dynamic factor is less by 21.7%: $\frac{\chi -{\chi }_c}{\chi }\times 100\%=\frac{3-2.35}{3}\times 100\%=21.7\%$

Weight of the composite beam is less by 25.7%: $\frac{W-W_c}{W}\times 100\%=\frac{175-130}{175}\times 100\%=25.7\%$

Height of the composite beam is less by 3.8%: $\frac{d-d_c}{d}\times 100\%=\frac{20-19.25}{20}\times 100\%=3.8\%$

If we decrease grade of the steel for the base member for the example considered above, from fy=60 ksi To fy=40 ksi , the effect of the proposed composite beam will be higher:

Dynamic factor will be 35% less,

Weight of the composite beam will be 32% less and

Height of the beam will be 7% less.

The amount dissipated energy is increased by increasing the ductility of the structure.

In the analysis above, we have neglected by inertial forces in order to simplify approach and formulas. For the real seismic or dynamic impact the effect of inertial forces for the composite reinforcing beam, according to the present invention, will be even more, because the composite beam has more ductility than a traditional beam.

It will be understood that each of elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in composite structures and dynamic/seismic resistant of the structures provided therewith, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

Claims

1. An impact resistant composite metal structure comprising a base member and a plurality of high-strength reinforcing elements embedded in said base member in longitudinal direction.

2. An impact resistant composite metal structure as defined in claim 1, wherein the said reinforcing elements are embedded flush with the surface of the said base member in tensile stress zone and in compression zone if a thickness of the said base member is less than three effective diameters of the said reinforcing elements.

3. An impact resistant composite metal structure as defined in claim 1, wherein the said reinforcing elements in compression stress zone are embedded in channels below surface of the said base member if a thickness of the said base member is more than three effective diameters of the reinforcing elements; the channels in the said base member are milled directly before the reinforcing elements are embedded during the hot rolling of base member, and the channels are pressed in directly after the reinforcing elements are embedded in the channels.

4. An impact resistant composite metal structure as defined in claim 1, wherein said reinforcing elements are spaced from one another by a distance that is a multiple of transverse size of the said reinforcing elements and percent of area of the reinforcing elements from the total cross section area of the composite structure is in a range of 3%-7.5%.

5. An impact resistant composite metal structure as defined in claim 1, wherein the said reinforcing elements are deformed round bars, strands or elements with square, rectangular, triangular or trapezium shape of cross section; the said reinforcing elements are embedded in the base member.

6. An impact resistant composite metal structure as defined in claim 1, wherein the said reinforcing elements are made with bosses distributed around the surface of the reinforcing elements in longitudinal direction.

7. An impact resistant composite metal structure as defined in claim 1, wherein the said reinforcing elements with triangular or trapezium shape of cross section are embedded with widest base of the reinforcing elements at the bottom of the channels.

8. An impact resistant composite metal structure as defined in claim 1, wherein the said base member can be used with all standard wrought forms, including W-beam, structural tubing and pipe or can be assembled from the standard forms as a built-up section.

9. An impact resistant composite metal structure as defined in claim 1, wherein the said base member made of metal plate, the said reinforcing elements are embedded in said base member in longitudinal direction.

10. An impact resistant composite metal structure as defined in claim 1, wherein the said base member is extruded with channels and the said reinforcing elements are embedded in these channels during the extrusion process or right after it.

11. An impact resistant composite metal structure as defined in claim 1, wherein the said the reinforcing elements are embedded in a mould for the base member and a liquid metal is poured into the mould.

12. An impact resistant composite metal structure as defined in claim 1, wherein the said the reinforcing elements are embedded into a cast for the base member and the structure with reinforcing elements is pressed or rolled under high pressure.

13. An impact resistant composite metal structure as defined in claim 1, wherein the said base member made of metal pipe and loaded with eccentric compression loads, said reinforcing elements equally distributed around external perimeter of the pipe in longitudinal direction and they are embedded flush by pressing in during of a hot rolling or extrusion process.

14. An impact resistant composite metal structure as defined in claim 1, wherein the said reinforcing elements are embedded in the pipe base member in a helical longitudinal arrangement.

15. An impact resistant composite metal structure as defined in claim 1, wherein the said reinforcing elements are made as mesh matrix and the matrix is embedded around external surface of the pipe base member by pressing in during a hot rolling process; directions of the reinforcing elements in matrix shall be less than 45 degrees with the longitudinal direction of the pipe.

16. An impact resistant composite metal structure as defined in claims 1, wherein the said pipe base member with the embedded reinforcing elements after a cooling is inserted in another hot pipe, having interior diameter tittles more than exterior diameter of the said pipe base member.

17. An impact resistant composite metal structure as defined in claim 1, wherein the said pipe base member with the embedded reinforcing elements filled out with concrete forming a Lally column.