7.2. Reinforcement

This paragraph contains information on the material properties of reinforcement steel.

Strength and stiffness

Material properties (bars)

Table 7.2 Material properties for reinforcement steel in concrete.

Steel Grade	Tensile Strength \(( f_{t;k} )\) [N/mm²]	Yield Stress \(( f_{y;k} )\) [N/mm²]	Strain at Maximum Load \(\varepsilon_{su}\) [‰]
FeB 400 HWL, HK	400	350	4.00
FeB 500 HWL, HK	500	435	3.25
FeB 500 HKN	500	435	2.75

Material properties (nets)

Table 7.3 Material properties reinforcement steel nets.

Steel Grade	Tensile Strength \(( f_{t;k} )\) [N/mm²]	Design value tensile strength \(( f_{y;k} )\) [N/mm²]	Strain at Maximum Load \(\varepsilon_{su}\) [‰]
FeB 500 HKN, HWN	500	435	2.175

Reinforcement areas for beams and columns

Table 7.4 Steel reinforcement areas.

Diameter \(\phi\) [mm]	\(A_s\) [mm^2]
	1 bar	2 bars	3 bars	4 bars	5 bars	6 bars	7 bars	8 bars	9 bars	10 bars
6	28	57	85	113	141	170	198	226	254	283
8	50	101	151	201	251	302	352	402	452	503
10	79	157	236	314	393	471	550	628	707	785
12	113	226	339	452	565	679	792	905	1018	1131
16	201	402	603	804	1005	1206	1407	1608	1810	2011
20	314	628	942	1257	1571	1885	2199	2513	2827	3142
25	491	982	1473	1963	2454	2945	3436	3927	4418	4909
32	804	1608	2413	3217	4021	4825	5630	6434	7238	8042

Reinforcement in nets for slabs

Table 7.5 Reinforcement nets in slabs.

Spacing (c.t.c.) [m]	Bars/length [1/m]	Total area per meter width [mm²/m]
		\(\phi = 6 [mm]\)	\(\phi = 8 [mm]\)	\(\phi = 10 [mm]\)	\(\phi = 12 [mm]\)	\(\phi = 16 [mm]\)	\(\phi = 20 [mm]\)	\(\phi = 25 [mm]\)
70	14.29	404	718	1122	1616	2873	4489	7015
75	13.33	377	670	1047	1508	2680	4188	6543
80	12.50	353	628	982	1414	2513	3927	6136
85	11.76	333	591	924	1330	2365	3695	5773
90	11.11	314	558	873	1257	2234	3490	5454
95	10.53	298	529	827	1191	2117	3308	5169
100	10.00	283	503	785	1131	2011	3142	4909
105	9.52	269	479	748	1077	1914	2991	4673
110	9.09	257	457	714	1028	1828	2856	4462
115	8.70	246	437	683	984	1749	2733	4271
120	8.33	236	419	654	942	1675	2617	4089
125	8.00	226	402	628	905	1609	2513	3927
130	7.69	217	387	604	870	1546	2416	3775
135	7.41	210	373	582	838	1490	2328	3637
140	7.14	202	359	561	808	1436	2243	3505
145	6.90	195	347	542	780	1387	2168	3387
150	6.67	189	335	524	754	1341	2095	3274
155	6.45	182	324	507	730	1297	2026	3166
160	6.25	177	314	491	707	1257	1964	3068
165	6.06	171	305	476	685	1218	1904	2975
170	5.88	166	296	462	665	1182	1847	2886
175	5.71	161	287	449	646	1148	1794	2803
180	5.56	157	280	437	629	1118	1747	2729
185	5.41	153	272	425	612	1088	1700	2656
190	5.26	149	264	413	595	1058	1653	2582
195	5.13	145	258	403	580	1031	1612	2518
200	5.00	141	251	393	566	1005	1571	2454
250	4.00	113	201	314	452	804	1257	1964

Note

In concrete plates (floors and walls) the reinforcement is usually specified as the the type of bar and the spacing (Ø12-200) rather than the number of bars per meter (5 Ø12)

Lab splice length

In some cases the reinforcement bars need to be coupled because of the limited lengths of the bars or to ease execution. This is done by placing two bars relatively close to each other for a certain lap length. The forces are transmitted by shear and compressive stresses in the concrete. For a first design the lap length can be estimated as:

40 x Ø (diameter smallest bar)

For exact calculations, see EC2

Fig. 7.1 Lab splice length in reinforced concrete.

Cover

Table 7.6 Concrete cover per structural element.

Structural Element	Cover c [mm] per environment			Increase [mm]
	dry	wet	salt or aggresive	modified surface	uninspected table surface
Plaat en wand	15	25	30	+5	+5
Balk, poer en console	25	30	35	+5	+5
Kolom	30	35	40	+5	+5

Note

Further demands:
c ≥ Ø (for bars ≤ Ø 25 mm)
c ≥ 1,5Ø (for bars > Ø 25 mm)
prestressing steel: + 5 mm

Under certain conditions it is allowed to bundle 2 of three bars together without spacing. These bundles can be regarded as a single bar with the same cross section (mm2 ) as the total bundle.

Fig. 7.2 Reinforced concrete cover.

Minimal bar distances

The spacing between (not c.t.c distance) the bars should be not less than the maximum of:

• the bar diameter

• the maximum aggregate size + 5 mm

• 20 mm

When bars are placed in separate layers, care must be taken that good compaction of the concrete must be possible. In the case of walls there must be enough room to cast concrete in the lower regions of the wall. At laps the distances between the bars may be smaller.

Fig. 7.3 Minimal bar distances in reinforced concrete.